John Stott:

‘The author of Psalm 139 looks back to the antenatal stage of his existence. Three words sum up what he affirms. First, creation. He seems to liken God both to a potter who “formed” his inmost being and to a weaver who “knit him together” in his mother’s womb (v. 13). Although the Bible makes no claim to be a textbook of embryology, here is a plain affirmation that the growth of the fetus is neither haphazard nor automatic but a divine work of creative skill.

‘The second word is continuity. The psalmist surveys his life in four stages: past (v. 1), present (vv. 2–6), future (vv. 7–12), and before birth (vv. 13–16), and in all four refers to himself as “I.” He who is writing as a full-grown man has the same personal identity as the fetus in his mother’s womb. He affirms a direct continuity between his antenatal and postnatal being.

‘The third word is communion, or relationship. Psalm 139 is arguably the most radical statement in the Old Testament of God’s personal relationship to the individual. Personal pronouns and possessives occur in the first person (I, me, my) 46 times and in the second person (you, yours) 32 times. Further, the basis on which God knows us intimately (vv. 1–7) and attaches himself to us so that we cannot escape from him (vv. 7–12) is he formed us in the womb and established his relationship with us then (vv. 13–16).’

These three words supply us with the essential biblical perspective in which to think. The fetus is not a growth in the mother’s body (which can be removed as readily as her tonsils or appendix), nor even a potential human being, but a human life who, though not yet mature, has the potentiality to grow into the fulness of the humanity he already possesses.

Christ the Cornerstone: Collected Essays of John Stott, 294f.