What does it mean that "You formed my inward parts" (Psalm 139:13)?

from the old testament

• The statement “you formed my inward parts” appears in the middle of Psalm 139. The Psalm opens with, “O LORD, you have searched me and known me!“ (Psalm 139:1). This statement grounds the rest of the Psalm, where David will express how God knows Him and what the implications of that are.
• In the first section, God knows David’s everyday activities. “You know when I sit down and when I rise up; you discern my thoughts from afar” (Psalm 139:2a). He also knows what David is thinking, “you discern my thoughts from afar” (Psalm 139:2b). Because of His great knowledge, God is “acquainted with all my ways” (Psalm 139:3). Indeed, “Even before a word is on my tongue, behold, O LORD, you know it altogether.” (Psalm 139:4). God’s knowledge implies that He is guiding David (Psalm 139:5), leading David to marvel, “Such knowledge is too wonderful for me” (Psalm 139:6).
• In the second section, David realizes that God’s knowledge means there is nowhere one can hide from Him. He asks the rhetorical question, “Where shall I go from your Spirit? Or where shall I flee from your presence?” (Psalm 139:7). The answer? Nowhere. Even if David could go into the highest or lowest places, God is there (Psalm 139:8). If he were to travel to the most remote locations or depths of the seas, God is there and leading David (Psalm 139:9–10). Even if David feared that darkness would hide him from God, it isn’t so for “even the darkness is not dark to you; the night is bright as the day, for darkness is as light with you.” (Psalm 139:11–12).
• It is in the third section where the statement, “you formed my inward parts,” is found, and begins a transition in the Psalm. Until now, David appears to be talking about God’s observational knowledge, that God knows David because He’s been watching him. But now David comes closer to home: God’s knowledge is intimate. “For you formed my inward parts; you knitted me together in my mother’s womb” (Psalm 139:13). David says that God knows him because He created him. David praises God with the famous line: “I am fearfully and wonderfully made” (Psalm 139:14).
• Indeed, David goes further. Not only did God create Him in his mother’s womb, but He saw his frame and formless body (Psalm 139:15–16a). Even before He started forming David, “Your eyes saw my unformed substance; in your book were written, every one of them, the days that were formed for me, when as yet there was none of them” (Psalm 139:16b).
• The first three sections set the stage for David’s response and confidence in the remaining three short sections. Because God knows everything both observationally and intimately, David praises God’s infinite wisdom (Psalm 139:17–18); expects God to judge his enemies (Psalm 139:19–22); and desires God to guide him to righteousness (Psalm 139:23–24).
• While David was talking about himself, what he expressed is what the rest of the Old Testament teaches about humanity in general. God told Jeremiah, “Before I formed you in the womb I knew you, and before you were born I consecrated you; I appointed you a prophet to the nations” (Jeremiah 1:5), exemplifying that God both forms people and plans their futures (Job 14:5). As our Creator, God also judges between right and wrong, training us all through Scripture how to live in a way that pleases Him (Psalm 119:105).

from the new testament

• In the New Testament, we continue to learn that God knows all of us. Speaking of the Father, Jesus said, “even the hairs of your head are all numbered” (Matthew 10:30). Hairs are insignificant, which shows just how intimately familiar God is with us.
• We also learn that God has a special place for humanity that is different than the rest of His creation. This is why Jesus added a true human nature, knitted together in Mary’s womb to be born like us (Luke 1:31), so that He could save us (Matthew 1:21).
• We learn that though Scripture teaches us what pleases God, that none of us can do so (Romans 8:8) and that we all sin (Romans 3:23). Jesus, however, in His humanity lived exactly like us but without sin (Hebrews 4:15). Because of that, He was able to die to take the punishment our sins deserved so that we who repent and believe in Him will live forever (John 3:16).
• As believers, we learn that God counts Jesus’ righteousness as our righteousness (Romans 4:5) and that, as new creations (2 Corinthians 5:17), we are finally able to live righteously by abiding in Jesus (John 15:4–5). In this way, God has fulfilled what David prayed for himself: in Jesus, we learn to live all the days of our lives righteously.

implications for today

God is personally involved in everyone's life. He knows each of us better than we know ourselves, having been there from the moment of conception. Even while David was an “unformed substance” in his mother’s womb, God had already considered him a full-fledged person and had already mapped out his life.

We can learn from this. First, unborn children are full-fledged people in God's eyes. They are not masses of tissue. Yes, they are still being formed, but it is God who is forming them. Any intentional act of stopping the life God is creating is both an act of violence against another person and an act of rebellion against God.

Second, you are not an accident—no matter the circumstances of your birth! God formed you. Yes, we know that your formation involved genetics and DNA. But God both created that process and guided it in you. Your true identity, then, is grounded in being personally created by God.

Third, your life has purpose because the God who formed you also numbered your days and calls you to live for Him. Every ability, opportunity, relationship, and season of life is meant to be lived in light of the One who created you. Psalm 139 reminds us that we are not self-made people drifting through random existence—we are people intentionally crafted by God and fully known by Him. Our value is not determined by success, appearance, popularity, or the opinions of others but by the God who knit us together with care. Because of that, we should live for Him, using the time and life God has given us to trust Him, follow Him, and glorify Him.