Psa 51:5 (v. 7 in the Hebrew; 50:7 in the LXX) reads as follows in the KJV:
Behold, I was shapen in iniquity, and in sin did my mother conceive me.
Many have used this passage to support the various theories of Original Sin. Notwithstanding, such is not in view in this passage. As one Protestant scholar noted:
This verse has been especially popular with Christian expositors, who have used it in connection with the doctrine of original sin (see Dalglish, Psalm Fifty-One, 118–23; Zink, VT 17 [1967] 354–61). Some interpreters have understood the sin involved as that of sexual passion or sexual intercourse, and perhaps even adultery on the part of the mother. Attention is focused on יחם, “to be hot/rut/conceive.” Delitzsch (157) flirts with the attraction of this view when he says that the verb “hints at the beast-like element in the act of coition,” though he does not adopt it. This interpretation is augmented by the widespread interpretation of the “knowledge of good and evil” in Gen 3 as sexual intercourse and by references that declare sexual acts, bodily discharges, and birth to be ritually unclean (Exod 21:9; Lev 12; 15; etc.). A modern Jewish scholar, Y. Kaufmann (The Religion of Israel, from Its Beginnings to the Babylonian Exile, tr. M. Greenberg [Chicago: University of Chicago Press, 1969], 293–94), illustrates this approach when he argues that sexual desire is the archetypical sin in Gen 3, “the characteristic mark of the evil impulse.” Procreation becomes not a blessing (as in Gen 1:28), but the result of sin. “The sexual act … is the child of sin. Offspring was given to man only after he had sinned and became subject to death.… The race was born from sin.” Kaufmann applies this interpretation to Ps 51:5, “Man was created by grace, but is born through sin.” More recently Caquot (RHR 1969 [1966] 144–45) interprets v 5 as applying to Jerusalem as the “mother” of the Israelites. He suggests that the background is found in the sexual symbolism used in Hos 2:6–9; Ezek 16:3; 23:25 (also note Isa 50:1; 64:1–8; Jer 50:1–12). He notes that the coarseness of the verb with its bestial application would be appropriate if sinful and adulterous Jerusalem is in mind.
However, this influential interpretation is dubious. That sexual desire is the “archetypal sin” of Gen 3 is very doubtful (see commentaries). Dalglish points out that “nowhere in the Old Testament is the legitimate act of coition referred to as sinful” (Psalm Fifty-One, 119). Such passages as Gen 1:28; 9:1, 7; 29:31; 30:22, 23; Ruth 4:13; Job 10:8–12; Ps 139:13–16 make it extremely difficult to maintain any inherent sinfulness in sexual intercourse, conception, and birth. Admittedly, the verb is used elsewhere of animals (Gen 30:38, 39, 41; 31:10; the more common verb is הרה) and one can understand Delitzsch’s “hint.” But it occurs only six times, and too much should not be built on such limited usage. Caquot’s case for Jerusalem is possible, but far from certain. Regardless of the identity of the mother, her sexual passion is not the central focus of the confession. The suppliant is not confessing a mother’s sin. The emphasis is on personal sinfulness: “For my acts of rebellion, I know indeed … against you, you only, I have sinned.”
The passage is more commonly understood today as a confession of the essential human condition of the speaker. “One is a sinner simply as a result of one’s natural human descent” (W. Eichrodt, Theology of the Old Testament, I, 268). Closely related to this approach is what may be called the social view. “It is the tragedy of man that he is born into a world full of sin” (Weiser, 405; also A. A. Anderson, 395). No particular sinfulness of the mother or the process of conception is involved. The emphasis is on the sin of the speaker, who admits that sin has been “no freak event” (Kidner, 190), but goes back to the roots of personal existence (see Ps 58:3). Thus the psalm reflects acceptance of the understanding that human life always involves sin and guilt (see Gen 8:21; Job 14:4; 15:14–16; 25:4; Ps 143:2; John 3:6; Kraus, 544).
J. K. Zink has taken up the interpretations of various Jewish commentators and argued that 51:5 and Job 14:4 should be understood in the sense of ritual uncleanness. This approach links these verses to laws on uncleanness and purification after sexual intercourse (Lev 15:18). Zink (VT 17 [1967] 360) points out that the Levitical laws frequently use “sin” and “uncleanness” as synonyms and argues that “iniquity” and “sin” in 51:7 should be understood in the same way (note the “cleanse me” in v 2). Thus the confession is concerned with a birth that occurred in the “sinful” state of disqualification from participation in ritual worship.
The best interpretation seems to be the second discussed above. However, the background of ritual impurity enhances the force of the confession and properly deserves attention. Further, the verse may indeed have been understood with Jerusalem as the mother after the re-interpretation of the psalm by the addition of vv 18–19. A purely ritual basis (as proposed by Zink) is too restricted for the comprehensive confession of sin. Such ritual uncleanness would be, after all, unavoidable on the part of every person (and could be used as an excuse). This is hardly adequate for the emphatically personal confession of rebellion and sin in vv 5–6. It is hardly probable that the ritual uncleanness of the worshiper’s mother at conception and childbirth would be continually before the speaker or that he or she should declare “against you, you only, I have sinned.” The main point is the comprehensive nature of the suppliant’s own sin. (Marvin E. Tate, Psalms 51-100 [Word Biblical Commentary vol. 20; Dallas: Word Books, 1998], 18-20)