Jamieson, Fausset and Brown on Song of Solomon 4:2

2. even shorn--the Hebrew is translated (1Ki 6:25), "of one size"; so the point of comparison to teeth is their symmetry of form; as in "came up from the washing," the spotless whiteness; and in "twins," the exact correspondence of the upper and lower teeth: and in "none barren," none wanting, none without its fellow. Faith is the tooth with which we eat the living bread (Joh 6:35, 54). Contrast the teeth of sinners (Psa 57:4; Pr 30:14); also their end (Psa 3:7; Mt 25:30). Faith leads the flock to the washing (Zec 13:1; 1Co 6:11; Tit 3:5).

none ... barren--(2Pe 1:8). He who is begotten of God begets instrumentally other sons of God.