Charles Ellicott Commentary 1 Samuel 17:47

"and that all this assembly may know that Jehovah saveth not with sword and spear: for the battle is Jehovah`s, and he will give you into our hand." — 1 Samuel 17:47 (ASV)

For the battle is the Lord’s ... —Although we possess no special ode or psalm composed by David on the occasion of this mortal combat, in which, owing to his sure trust in Jehovah, he won his never-to-be-forgotten victory, yet in many of the compositions attributed to him in the Psalter we find memories of this, his first great triumph. So in Psalm 44:6-8 we read—

“I will not trust in my bow,
Neither shall my sword save me.
In God we boast all the day long,
And praise thy Name for ever.”

And in Psalm 33:16-20,

“There is no king saved by the multitude of an host,
A mighty man is not delivered by much strength.”

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“Our soul waiteth for the Lord,
He is our help and our shield.”