The three oldest sons of Jesse had followed Saul to the battle. And the names of his three sons who went to the battle were Eliab the firstborn, and next to him Abinadab, and the third Shammah.
Forty days the two armies lay encamped facing one another, each advantageously posted, but neither forward to engage. Either they were parleying and treating of an accommodation or they were waiting for recruits; and perhaps there were frequent skirmishes between small detached parties.
Commenting on 1 Samuel 17:12-30
And the three eldest sons of Jesse went and followed Saul to the battle,.... Either of their own accord, or rather at their father's motion, or however with his knowledge and consent, who because he could not go himself, willed them to go; and these were forward, and some of the foremost that followed Saul to the battle, being zealous and well disposed to defend...
1Sa 17:12-15 1Sa 17:12-15 are closely connected with the preceding words, “All Israel was alarmed at the challenge of the Philistine; but David the son of that Ephratite (Ephratite, as in Rth 1:1-2) of Bethlehem in Judah, whose name was Jesse,” etc. The verb and predicate do not follow till 1Sa 17:15; so that the words occur here in the form of an anacolouthon.
Commenting on 1 Samuel 17:12-15