Jamieson, Fausset and Brown on Song of Solomon 4:3

3. thread--like a delicate fillet. Not thick and white as the leper's lips (type of sin), which were therefore to be "covered," as "unclean" (Le 13:45).

scarlet--The blood of Jesus Christ (Is 6:5-9) cleanses the leprosy, and unseals the lips (Is 57:19; Ho 14:2; He 13:15). Rahab's scarlet thread was a type of it (Jos 2:18).

speech--not a separate feature from the lips (Zep 3:9; Col 4:6). Contrast "uncircumcised lips" (Ex 6:12). Maurer and Burrowes translate, "thy mouth."

temples--rather, the upper part of the cheek next the temples: the seat of shamefacedness; so, "within thy locks," no display (1Co 11:5, 6, 15). Mark of true penitence (Ezr 9:6; Eze 16:63). Contrast Jr 3:3; Eze 3:7.

pomegranate--When cut, it displays in rows seeds pellucid, like crystal, tinged with red. Her modesty is not on the surface, but within, which Jesus Christ can see into.