And when Saul went forth with the hosts, he said, “God will try you with a river; whoever drinks of it, is not of me, and whoever tastes it not, he is of me, except for him who scoops up with his hand.
The allusion in this verse is that God (سبحانه) tests human beings in their association with others, with this world, and with the lower self. There are some whose association with these things is limited to that which is required for [them to earn a] basic livelihood and what is necessary for their salvation and security. There are others who go beyond the limit of what is required, and extend their association with things of the world, self, and creation for the sake of carnal desire and their own preference.
There is nothing from God in that which involves doing a prohibited thing. There is nothing from this path (Ṭarīqa) in that which involves holding on to more than what is needed.
But they drank of it, except a few of them;
Likewise the elect in every moment are few in their number but sublime in their worth.
and when he crossed it, with those who believed, they said, “We have no power today against Goliath and his troops.”
They viewed the situation with the eye of the external world and were overcome with mortal fright. God fortified their hearts, telling them that the Real (سبحانه) helps His friends, if He wills it.
Those who thought they would meet God, said, “How often a small company has overcome a numerous one, by God's leave; and God is with the patient.”
[The victory is] not by them, but by the permission of God through what He has willed, and through His aid and His help. God is with the patient through help, support, and strength.