Charles H. Spurgeon on Psalms 139:13

Thou hast covered me in my mother's womb. The word here rendered cover means properly to interweave; to weave; to knit together, and the literal translation would be, "Thou hast woven me in my mother's womb", meaning that God had put his parts together, as one who weaves cloth, or who makes a basket. So it is rendered by De Wette and by Gesenius (Lex.). The original word has, however, also the idea of protecting, as in a booth or hut, woven or knit together, —to wit, of boughs and branches. The former signification best suits the connection; and then the sense would be, that as God had made him —as he had formed his members, and united them in a bodily frame and form before he was born —he must be able to understand all his thoughts and feelings. As he was not concealed from God before he saw the light, so he could not be anywhere. —Albert Barnes.