Fighting in defense of Truth and Right is not to be undertaken lightheartedly, nor to be evaded as a duty. Life and Death are in the hands of God. Not all can be chosen to fight for God. It requires constancy, firmness, and faith. Given these, large armies can be roused by those who battle for God, as shown by the courage of David, whose prowess single-handedly disposed of the Philistines. The mission of some of the messengers, like Jesus, was different -- less wide in scope than that of Mustafa, and He carries it out as He wills.

David and Goliath [2:243-253]

Hast thou not regarded those who went forth from their habitations in their thousands fearful of death? God said to them, 'Die!' Then He gave them life. Truly God is bounteous to the people, but most of the people are not thankful. So fight in God's way, and know that God is All-hearing, All-knowing. Who is he that will lend God a good loan, and He will multiply it for him manifold? God grasps, and outspreads; and unto Him you shall be returned.

Hast thou not regarded the Council of the Children of Israel, after Moses, when they said to a Prophet of theirs, 'Raise up for us a king, and we will fight in God's way.' He said, 'Might it be that, if fighting is prescribed for you, you will not fight?' They said, 'Why should we not fight in God's way, who have been expelled from our habitations and our children?' Yet when fighting was prescribed for them, they turned their backs except a few of them; and God has knowledge of the evildoers. 

Then their Prophet said to them, 'Verily God has raised up Saul for you as king.' They said, 'How should he be king over us who have better right than he to kingship, seeing he has not been given amplitude of wealth?' He said, 'God has chosen him over you, and has increased him broadly in knowledge and body. God give the kingship to whom He will; and God is All-embracing, All-knowing.' 

And their Prophet said to them, 'The sign of his kingship is that the Ark will come to you, in it a Shechina from your Lord, and a remnant of what the folk of Moses and Aaron's folk left behind, the angels bearing it. Surely in that shall be a sign for you, if you are believers.' 

And when Saul went forth with the hosts he said, 'God will try you with a river; whosoever drinks of it is not of me, and whoso tastes it not, he is of me, saving him who scoops up with his hand.' But they drank of it, except a few of them; and when he crossed it, and those who believed with him, they said, 'We have no power today against Goliath and his hosts.' Said those who reckoned they should meet God, 'How often a little company has overcome a numerous company, by God's leave! And God is with the patient.' 

So, when they went forth against Goliath and his hosts, they said, 'Our Lord, pour out upon us patience, and make firm our feet, and give us aid against the people of the unbelievers!' And they routed them, by the leave of God, and David slew Goliath; and God gave him the kingship, and Wisdom, and He taught him such as He willed. Had God not driven back the people, some by the means of others, the earth had surely corrupted; but God is bounteous unto all beings.

These are the signs of God We recite to thee in truth, and assuredly thou art of the number of the Envoys. And those Messengers, some We have preferred above others; some there are to whom God spoke, and some He raised in rank.