Their third prayer was that Allah might help them to be...
Their third prayer was that Allah might help them to be victorious against those infidels. That was, of course, the result or the reward of those two qualities: i.e. patience and perseverance, and being firm in the battlefield. Bible says: "And it was so, that when he (Saul) had turned his back to go from Samuel, God gave him another heart." "And the spirit or God came upon him and he prophesied.
[^2] There is some similar incident mentioned in the Bible[^3] of trying the people with thirst, but that is a different incident. It was when Gideon tried his forces by the 'Well of Harod '. The trial of the people under Saul was by the river.
From this verse it becomes clear that the one who leads the people should have inspired knowledge of good and evil for his followers and be able to conduct trials of the people's faith as was Saul who directed his men not to drink more than one handful of water from the river, even though they were dying of thirst. It was only a trial that a few, who were true believers, succeeded and Allah helped them to win Goliath and his troops.
"Thus they routed them by Allah's leave, and David slew Goliath; and Allah gave him the kingship and wisdom and taught him of that He willed. And were Allah not to repel some people by means of other people, the earth would certainly be full of mischief; but Allah is Gracious to all (His) creatures." It is completely certain that Allah will not leave such believers alone, although the number of them be small and the number of their enemy be large.
That is why the verse expresses that they set out to fight against them and it was by the leave of Allah that they defeated he enemy. It says: **"** Thus they routed them by Allah's leave..." David, who was a very young lad, but was vigorous and brave, had attended the army of Saul to fight against the enemy. He succeeded to all Goliath. "...and David slew Goliath..." The young warrior threw one or two stones by means of a sling which he had with him, towards Goliath.
He utilized the sling so skillfully that the stone hit just upon the head and pierced the forehead of Goliath. So, Goliath cried loudly and fell down on the ground. At that moment, fear and terror rushed into the hearts of his troops. They began to flee.