Answer
The Bible does not indicate that David was an illegitimate son of Jesse, i.e., that he was the result of his father having an adulterous affair. There are three primary passages in Scripture, however, that lead some to speculate that David might have been born out of wedlock.
In 1 Samuel chapter 16, the prophet Samuel went to Bethlehem to anoint one of Jesse’s sons as the next king of Israel (1 Samuel 16:1), but David was not initially invited to the feast. Instead, David was still shepherding the family’s sheep while the feast was taking place. Samuel had to ask Jesse, “Are these all the sons you have?” (1 Samuel 16:11). The oversight could possibly be due to David being considered a lesser or illegitimate member of the family. However, Jesse states that David was not there because he was the youngest. Nothing about him being illegitimate is even hinted at.
In 1 Samuel chapter 17, before David’s battle with Goliath, David visits the site of the battle and is harshly rebuked by Eliab, the oldest of his brothers. Eliab “burned with anger” at David and accused him of being “conceited” and having a wicked heart (1 Samuel 17:28). It seems strange for Eliab to be that hostile toward David—perhaps Eliab viewed David as an outsider and not truly part of the family. However, his rudeness could easily be due to his anger over David being anointed as the next king of Israel instead of him. It could also be explained by the fact that David was the youngest. Eliab and David would not be the first set of oldest and youngest siblings to clash.
In Psalm 51:5, David says, “Behold, I was brought forth in iniquity, and in sin did my mother conceive me” (ESV). This verse could possibly be understood as David saying that the very act of his conception was sinful, i.e., he was the result of an adulterous union. Most Bible scholars, though, believe David is referring to his own sin, not his mother’s. He is saying that he was sinful from the moment he was conceived, not that the act of his conception itself was sinful. As the NIV reads, “Surely I was sinful at birth, sinful from the time my mother conceived me.”
The most that can be said from these passages is that it is possible that David was illegitimate. It is far more likely, however, that David’s poor relationship with his brothers was due to standard sibling rivalry, compounded by the fact that God had chosen him to be king. Psalm 51:5, in context, seems to be David’s recognition that he had always been sinful, that there was never a moment in his existence when he wasn’t in need of God’s grace.
Answering the question of whether David was illegitimate appears to be a matter of “do not go beyond what is written” (1 Corinthians 4:6). And, ultimately, David’s illegitimacy is irrelevant to why God called him to be the king of Israel: “After removing Saul, he made David their king. God testified concerning him: ‘I have found David son of Jesse, a man after my own heart; he will do everything I want him to do’” (Acts 13:22).