Old Testament readings use the Septuagint , the Scripture the apostles quoted. Masoretic numbering shown for reference.Learn why
LXX

1 Samuel 17:20

[And David rose early in the morning, and left the sheep to a keeper, and took and went as Jessae commanded him, and he came to the trench and to the army as it was going out to fight, and they shouted for the battle. ]

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