Sincerity
Sincerity in the UPDV is the absence of guile in the spirit and the singleness of the heart in the way it serves, loves, believes, and speaks. It is the opposite of duplicity — of the smooth mouth that hides a heart at war, of the feigned mourner, of the spy who pretends to be righteous, of the one who walks humbly outwardly but inwardly is full of deceit. The word the UPDV uses across the Pauline epistles is straight: serve "in sincerity and in truth" (Jos 24:14), keep the feast "with the unleavened bread of sincerity and truth" (1Co 5:8), let love be "without hypocrisy" (Ro 12:9), faith "unfeigned" (1Ti 1:5), love "incorruptible" (Eph 6:24). Behind those Pauline turns of phrase stands a Psalm beatitude — "Blessed is [the] man to whom Yahweh does not impute iniquity, And in whose spirit there is no guile" (Ps 32:2) — and behind that, an OT moral instinct that ties uprightness of heart to safety, light, and shield.
In Whose Spirit There Is No Guile
The clearest single-verse anchor is the Psalm beatitude. "Blessed is [the] man to whom Yahweh does not impute iniquity, And in whose spirit there is no guile" (Ps 32:2). Forgiveness and guilelessness lie alongside each other; the man whose iniquity is not imputed is the same man with no guile in his spirit. The same diagnostic moves into the gospel: Jesus, seeing Nathaniel approach, says, "Look, an Israelite indeed, in whom is no guile!" (Joh 1:47). The same descriptor falls on Jesus himself, in 1 Peter's recall of Isaiah's servant — "who did no sin, neither was guile found in his mouth" (1Pe 2:22). Across these three references the word holds steady: no guile in spirit, no guile in the man approaching, no guile in the mouth of the suffering servant.
Singleness of Heart
Where "no guile" names what sincerity lacks, "singleness of heart" names what it has. Slaves are commanded to obey their masters according to the flesh, "with fear and trembling, in singleness of your⁺ heart, as to Christ" (Eph 6:5), "not in the way of eyeservice, as men-pleasers; but as slaves of Christ, doing the will of God from the soul; with goodwill serving as slaves, as to the Lord, and not to men" (Eph 6:6-7). The parallel passage in Colossians repeats the construction: "Slaves, obey in all things those who are your⁺ masters according to the flesh; not with eye-service, as men-pleasers, but in singleness of heart, fearing the Lord" (Cl 3:22). Singleness of heart is the antithesis of eye-service. Eye-service performs only when watched; singleness of heart serves the same way watched and unwatched, because the actual audience is the Lord. Zebulun's troops carry the same descriptor in OT idiom — "fifty thousand, and that could order [the battle array, and were] not of double heart" (1Ch 12:33). Not double-hearted, single-hearted: one allegiance, one direction.
Service in Sincerity and Truth
Joshua's farewell sets the OT keynote: "Now therefore fear Yahweh, and serve him in sincerity and in truth; and put away the gods which your⁺ fathers served beyond the River, and in Egypt; and serve⁺ Yahweh" (Jos 24:14). Service in sincerity is service that has put the rival gods away — the heart is not divided between Yahweh and the gods of Egypt, between Yahweh and the gods beyond the River. Hezekiah's prayer mirrors the same posture: "Remember now, O Yahweh, I urge you, how I have walked before you in truth and with a perfect heart, and have done that which is good in your sight" (Isa 38:3). The summary direction for any action sits in 1 Corinthians: "Whether therefore you⁺ eat, or drink, or whatever you⁺ do, do all to the glory of God" (1Co 10:31). One audience, one aim; sincerity is the unity of that direction across every act.
Sincere Love
Love is where the UPDV most often qualifies the noun with the adjective of sincerity. "Let love be without hypocrisy" (Ro 12:9). "Seeing you⁺ have purified your⁺ souls in your⁺ obedience to the truth to unfeigned love of the brothers, love one another fervently from a pure heart" (1Pe 1:22). "[My] little children, let us not love in word, neither with the tongue; but in deed and truth" (1Jo 3:18). Love that is "without hypocrisy," "unfeigned," and "in deed and truth" is the same triple description from three different writers. Paul tests the Corinthians by the same metric — "I don't speak by way of commandment, but as proving through the earnestness of others the sincerity also of your⁺ love" (2Co 8:8); "Therefore show⁺ to them in the face of the churches the proof of your⁺ love, and of our glorying on your⁺ behalf" (2Co 8:24). Love toward Christ takes the same adjective: "Grace be with all those who love our Lord Jesus Christ with [a love] incorruptible" (Eph 6:24).
Faith Unfeigned
Sincerity attaches to faith in the same way it attaches to love. "But the end of the charge is love out of a pure heart and a good conscience and faith unfeigned" (1Ti 1:5). The same compound — pure heart, good conscience, unfeigned faith — recurs as a familial inheritance: "having been reminded of the unfeigned faith that is in you; which dwelt first in your grandmother Lois, and your mother Eunice; and, I am persuaded, in you also" (2Ti 1:5). Three generations, one undiluted faith.
Sincerity in the Preaching of the Gospel
Sincerity governs not only conduct and inward state but speech, especially the speech that delivers the good news. "For we are not as the many, corrupting the word of God: but as of sincerity, but as of God, in the sight of God, we speak in Christ" (2Co 2:17). The triple denial in Thessalonians frames the same posture negatively: "For our exhortation [is] not of error, nor of impurity, nor in guile: but even as we have been approved of God to be entrusted with the good news, so we speak; not as pleasing men, but God who proves our hearts. For neither at any time did we come in words of flattery, as you⁺ know, nor in a cloak of greed, God is witness" (1Th 2:3-5). Paul's summary of his own life and ministry doubles back on the noun itself: "For our glorying is this, the testimony of our conscience, that in simplicity and sincerity of God, and not in fleshly wisdom but in the grace of God, we behaved ourselves in the world, and more abundantly toward you⁺" (2Co 1:12). Doctrine is to model the same: Titus, "in all things showing yourself an example of good works; in your doctrine [showing] uncorruptness, gravity" (Tit 2:7). The new birth feeds on milk of the same character — "as newborn babies, long for the spiritual milk which is without guile, that you⁺ may grow by it to salvation" (1Pe 2:2).
Childlikeness
Childlikeness is sincerity at the level of disposition. "Truly I say to you⁺, Whoever will not receive the kingdom of God as a little child, he will in no way enter in it" (Mr 10:15; cf. Lu 18:16-17). David's psalm speaks the inward form: "Yahweh, my heart is not haughty, nor my eyes lofty; Neither do I exercise myself in great matters, Or in things too wonderful for me. Surely I have stilled and quieted my soul; Like a weaned child with his mother, Like a weaned child is my soul inside me" (Ps 131:1-2). Paul keeps the dispositional sense and adjusts the cognitive one: "Brothers, don't be children in mind: yet in malice be⁺ babes, but in mind be men" (1Co 14:20); "I would have you⁺ wise to that which is good, and simple to that which is evil" (Ro 16:19). The simple in the Psalms are those Yahweh preserves and instructs: "Yahweh preserves the simple: I was brought low, and he saved me" (Ps 116:6); "The opening of your words gives light; It gives understanding to the simple" (Ps 119:130).
The Unleavened Bread of Sincerity
Paul's strongest exhortation to the Corinthians arrives in feast-language: "therefore let us keep the feast, not with old leaven, neither with the leaven of malice and wickedness, but with the unleavened bread of sincerity and truth" (1Co 5:8). The matched-pair imperative in 1 Peter is plainer still: "Putting away therefore all wickedness, and all guile, and hypocrisies, and envies, and all evil speakings" (1Pe 2:1). Paul prays it for the Philippians: "so that you⁺ may approve the things that are excellent; that you⁺ may be sincere and void of offense to the day of Christ" (Phil 1:10). The eschatological qualifier — "to the day of Christ" — sets sincerity not as a momentary mood but as a posture sustained through to the day of judgment.
The Opposite: Duplicity
The UPDV's portrait of insincerity is concrete, narrative, and unsparing. "His mouth was smooth as butter, But his heart was war: His words were softer than oil, Yet they were drawn swords" (Ps 55:21). "For there is no faithfulness in their mouth; Their inward part is much wickedness; Their throat is an open tomb; They flatter with their tongue" (Ps 5:9). The serpent in Eden is "more subtle than any beast of the field" (Ge 3:1), and Paul writes the Corinthians fearing "lest by any means, as the serpent beguiled Eve in his craftiness, your⁺ minds should be corrupted from the simplicity and the purity that is toward Christ" (2Co 11:3). Old Testament narrative supplies the gallery: David at Achish's court, who "changed his behavior before them, and feigned himself insane" (1Sa 21:13); Joab sending the wise woman of Tekoa to "feign yourself to be a mourner" (2Sa 14:2); Jehu, who "did it in subtlety, to the intent that he might destroy the worshipers of Baal" (2Ki 10:19); the Gibeonites who "worked craftily, and went and made as if they had been ambassadors" (Jos 9:4); Jacob's hands disguised in goatskins (Ge 27:16); the spies who "feigned themselves to be righteous" to entrap Jesus (Lu 20:20), and his perception of "their craftiness" (Lu 20:23); the chief priests and scribes who "sought how they might take him with subtlety, and kill him" (Mr 14:1). Paul names the danger to disciples — "tossed to and fro and carried about with every wind of doctrine, by the sleight of men, in craftiness, after the wiles of error" (Eph 4:14). Sirach paints the same figure in slow motion: "There is a subtle [form of] craftiness which is unrighteous, And there is one who deceives people with kindness to gain a judgement" (Sir 19:25); "There is one who walks humbly and mournfully, But inwardly he is full of deceit" (Sir 19:26); "[There is one] with a downcast look, pretending to be deaf, But when unobserved he will get the better of you" (Sir 19:27); "Reproach will give you an evil name and shame to inherit; So [it will be with] an evil man [who is] double-tongued" (Sir 6:1).
Crookedness as the Opposite of Uprightness
What duplicity is in the heart, crookedness is in the way. "They have dealt corruptly with him, [they are] not his sons, [it is] their blemish; [They are] a perverse and crooked generation" (De 32:5). "The way of peace they don't know; and there is no justice in their goings: they have made crooked paths for themselves; whoever goes in them does not know peace" (Is 59:8); the wicked "are crooked in their ways, And wayward in their paths" (Pr 2:15); "as for such as turn aside to their crooked ways, Yahweh will lead them forth with the workers of iniquity" (Ps 125:5). The crafty tongue belongs to the same posture: "For your iniquity teaches your mouth, And you choose the tongue of the crafty" (Job 15:5).
Reward of the Upright
The upright in heart are the sincere of heart, and Wisdom literature attaches a long string of promises to them. "He lays up sound wisdom for the upright; [He is] a shield to those who walk in integrity" (Pr 2:7). "For the upright will stay in the land, And the perfect will be left in it" (Pr 2:21). "He who walks uprightly walks surely; But he who perverts his ways will be known" (Pr 10:9). "The house of the wicked will be overthrown; But the tent of the upright will flourish" (Pr 14:11). "Better is the poor who walks in his integrity, Than he who is perverse in [his] ways, though he is rich" (Pr 28:6). The Psalter answers: "My shield is with God, Who saves the upright in heart" (Ps 7:10); "Be glad in [the Speech of] Yahweh, and rejoice, you⁺ righteous; And shout for joy, all you⁺ who are upright in heart" (Ps 32:11); "Mark the perfect man, and look at the upright; For there is a [happy] end to the man of peace" (Ps 37:37); "the upright will have dominion over them in the morning" (Ps 49:14); "all the upright in heart will glory" (Ps 64:10); "Light is sown for the righteous, And gladness for the upright in heart" (Ps 97:11); "To the upright there rises light in the darkness: [He is] gracious, and merciful, and righteous" (Ps 112:4). Sirach extends the same line: "The gift of the righteous will stand forever; And his favor will prosper forever" (Sir 11:17); and Samuel's last witness — "From whom have I taken a bribe, or a pair of shoes?" — is sealed with the verdict, "he was found upright In the eyes of Yahweh, and in the eyes of all living" (Sir 46:19).
Sincerity Does Not Cancel Guilt
Abimelech's plea is the case in point. He answers Yahweh in a dream: "Didn't he say to me, She's my sister? And she, even she herself said, He's my brother. In the integrity of my heart and the innocence of my hands I have done this." Yahweh's reply concedes the integrity but not absolution: "Yes, I know that in the integrity of your heart you have done this, and I also withheld you from sinning against me. Therefore I didn't allow you to have any sex with her" (Ge 20:5-6). Sincerity is real and seen; it is also not the whole story. Abimelech is restrained from sin not by his own sincerity alone but by Yahweh's withholding hand.
Exemplars
The named exemplars come from across both testaments and both covenants. Zebulun's troops are "not of double heart" (1Ch 12:33). Hezekiah, on his deathbed, prays from "a perfect heart" (Isa 38:3). Nathaniel approaches Jesus and is greeted as "an Israelite indeed, in whom is no guile" (Joh 1:47). Paul appeals to his own life — "in simplicity and sincerity of God, and not in fleshly wisdom" (2Co 1:12). Timothy's "unfeigned faith" is traced back through "your grandmother Lois, and your mother Eunice" (2Ti 1:5). And Jesus, the model behind all the others, is the one in whose mouth no guile was found (1Pe 2:22).