The Quran

Preface

وَأَعِدّوا لَهُم مَا استَطَعتُم مِن قُوَّةٍ وَمِن رِباطِ الخَيلِ تُرهِبونَ بِهِ عَدُوَّ اللَّهِ وَعَدُوَّكُم وَآخَرينَ مِن دونِهِم لا تَعلَمونَهُمُ اللَّهُ يَعلَمُهُم ۚ وَما تُنفِقوا مِن شَيءٍ في سَبيلِ اللَّهِ يُوَفَّ إِلَيكُم وَأَنتُم لا تُظلَمونَ

Yusuf Ali

Against them make ready your strength to the utmost of your power, including¹ steeds of war, to strike terror into (the hearts of) the enemies, of God and your enemies, and others besides, whom ye may not know, but whom² God doth know. Whatever ye shall spend in the cause of God, shall be repaid unto you, and ye shall not be treated unjustly.³

The immediate occasion of this injunction was the weakness of cavalry and appointments of war in the early fights of Islam. But the general meaning follows. In every fight, physical, moral, or spiritual, arm yourself with the best weapons and the best arms against your enemy, so as to instil wholesome respect into him for you and the Cause you stand for.
There are always lurking enemies whom you may not know, but whom God knows. It is your duty to be ready against all, for the sacred Cause under whose banner you are fighting.
Be always ready and put all your resources into your Cause. You do not do so in vain. God’s reward will come in various forms. He knows all, and His reward will always be more generous than you can possibly deserve.