But thou art he, &c.— It was by the particular order of his Father that Christ came into the world; and therefore he said at his entrance into it, Sacrifice and offering thou wouldest not, but a body hast thou prepared me: Hebrews 10:5. When I was upon my mother's breasts, evidently relates to the miraculous order which God gave to Joseph and Mary to carry into Egypt the young child Jesus, who as yet hanged upon his mother's breasts, Matthew 2:20-21. I was cast upon thee from the womb, means that God took him at his birth, and in a particular manner charged himself with the care of him. It was anciently the custom, when a child was born, to lay it upon the ground; and then he who lifted it from thence thereby declared himself to be its father, and took upon himself the care of its maintenance. See Genesis 30:3; Genesis 50:23. Therefore when the poets would exaggerate the happiness of a man to whom all things succeeded according to his desire, they said, that he was taken up by some god or goddess.
Related Commentaries of Psalms 22:9
Psalms 22:9-10
9 But thou art he that took me out of the womb: thou didst make me hope when I was upon my mother's breasts.
10 I was cast upon thee from the womb: thou art my God from my mother's belly.