How do we know David was a true believer despite his sin?

David’s life is a profound illustration of the complexities of being a believer. While his actions in 2 Samuel 11 reveal significant moral failings, it is his response to those failures that confirms his faith. He is described as 'a man after God's own heart' (1 Samuel 13:14), which implies a relationship with God that is sincere and real. His repentance, as articulated in Psalms such as Psalm 51, demonstrates an acknowledgment of his sin and a plea for restoration. In Psalm 51:10, David cries out, 'Create in me a clean heart, O God,' reflecting a desire for holiness and an understanding that his actions had serious implications. This response, paired with God’s forgiveness, underscores that true believers may stumble, yet they return to God in genuine repentance, reaffirming their faith in His grace and mercy.