After that, to persuade Muslims to fight, they were told in verse 13 that there was no reason why they would not be ready to fight against the kind of people who had conspired to expel the Messenger of Allah. This refers to the Jews of Madinah who had hatched a plan to expel the Holy Prophet ﷺ from the city of Madinah. They had said: لَيُخْرِجَنَّ الْأَعَزُّ مِنْهَا الْأَذَلَّ (the one having more honor and power will certainly expel the one being humble and weak from there - 63:8). In their self-view, they were the people of honor and power while Muslims were weak and lowly. The answer they needed was given by Allah Al-mighty in His way. He took their proud statement as it was and made it come true in a manner that the Holy Prophet ﷺ and his Companions, by turning the Jews out of Madinah, proved that honor belonged to Muslims and disgrace to Jews.
Giving the second reason for fighting against them, it was said: وَهُم بَدَءُوكُمْ أَوَّلَ مَرَّةٍ (and it was they who started [ fighting ] against you for the first time). The sense is that they were the aggressors. What Muslims have to do now is simply to defend themselves, an action universally sane and normal.
Then, to remove the awe of the enemy from the hearts of Muslims, it was said: أَتَخْشَوْنَهُمْ ۚ فَاللَّـهُ أَحَقُّ أَن تَخْشَوْهُ (Do you fear them? Then, Allah is worthier that you fear Him) for there is no power that can cause His punishment to disappear. Finally, by saying: إِن كُنتُم مُّؤْمِنِينَ (if you are be-lievers), it was made clear that fearing anyone or anything other than Allah in a manner that obstructs the fulfillment of the injunctions of the Shari’ ah of Islam is not what a true believing-practicing Muslim would do.