Allah already knows those among you who keep back (men) from fighting (in Allah's cause), and those who say to their brethren, "Come here towards us," while they come not to the battle except a little (18)Being miserly towards you. Then when fear comes, you will see them looking to you, their eyes revolving like one over whom hovers death; but when the fear departs, they will smite you with sharp tongues, miserly towards good. Such have not believed. Therefore, Allah makes their deeds fruitless and that is ever easy for Allah.) Allah tells us that His knowledge encompasses those who sought to tell others not to go out and who said to their brethren, meaning their companions, friend and acquaintance (19)

هَلُمَّ إِلَيْنَا

(Come here towards us,) meaning, come to where we are in the shade and enjoying fruits. But in spite of that,

وَلَا يَأْتُونَ الْبَأْسَ إِلَّا قَلِيلًا - أَشِحَّةً عَلَيْكُمْ

(they come not to the battle except a little, being miserly towards you.) i.e., 'they are mean and have no love or mercy towards you.' As-Suddi said:

أَشِحَّةً عَلَيْكُمْ ۖ 

(Being miserly towards you.) means, with the booty.

فَإِذَا جَاءَ الْخَوْفُ رَأَيْتَهُمْ يَنْظُرُونَ إِلَيْكَ تَدُورُ أَعْيُنُهُمْ كَالَّذِي يُغْشَىٰ عَلَيْهِ مِنَ الْمَوْتِ ۖ 

(Then when fear comes, you will see them looking to you, their eyes revolving like one over whom hovers death;) means, because of the intensity of their fear and terror; this is how afraid these cowards are of fighting.

فَإِذَا ذَهَبَ الْخَوْفُ سَلَقُوكُمْ بِأَلْسِنَةٍ حِدَادٍ

(but when the fear departs, they will smite you with sharp tongues,) means, when security is restored, they will speak eloquently and nicely, claiming that they were the bravest and most chivalrous of men, but they are lying. Ibn 'Abbas, may Allah be pleased with him, said:

سَلَقُوكُمْ

(they will smite you) means, "they will start to talk about you." Qatadah said: "But when it comes to the booty, the most miserly of people and the worst to have to share the booty with are those who say, 'Give us, give us, we were there with you,' but during battle they were the most cowardly and the most likely to fail to support the truth." They are miserly towards good, meaning that there is no goodness in them, for they have combined cowardice with lies and little good. Allah says:

أُولَٰئِكَ لَمْ يُؤْمِنُوا فَأَحْبَطَ اللَّهُ أَعْمَالَهُمْ ۚ وَكَانَ ذَٰلِكَ عَلَى اللَّهِ يَسِيرًا

(Such have not believed. Therefore Allah makes their deeds fruitless and that is ever easy for Allah.)

يَحْسَبُونَ الْأَحْزَابَ لَمْ يَذْهَبُوا ۖ وَإِنْ يَأْتِ الْأَحْزَابُ يَوَدُّوا لَوْ أَنَّهُمْ بَادُونَ فِي الْأَعْرَابِ يَسْأَلُونَ عَنْ أَنْبَائِكُمْ ۖ وَلَوْ كَانُوا فِيكُمْ مَا قَاتَلُوا إِلَّا قَلِيلًا

(20. They think that the Confederates have not yet withdrawn; and if the Confederates should come, they would wish they were in the deserts among the bedouins, seeking news about you; and if they were to be among you, they would not fight but little.) This is another aspect of their abhorrent attribute of cowardice and fear:

يَحْسَبُونَ الْأَحْزَابَ لَمْ يَذْهَبُوا ۖ 

(They think that the Confederates have not yet withdrawn;) and that they are still close by and will return.

وَإِنْ يَأْتِ الْأَحْزَابُ يَوَدُّوا لَوْ أَنَّهُمْ بَادُونَ فِي الْأَعْرَابِ يَسْأَلُونَ عَنْ أَنْبَائِكُمْ ۖ 

(and if the Confederates should come, they would wish they were in the deserts among the bedouins, seeking news about you;) means, 'if the Confederates should come back, they hope that they will not be present with you in Al-Madinah, but that they will be in the desert, asking about news of you and what happened to you with your enemy.'

وَلَوْ كَانُوا فِيكُمْ مَا قَاتَلُوا إِلَّا قَلِيلًا

(and if they were to be among you, they would not fight but little.) means, 'if they are among you, they will not fight alongside you very much,' because they are so cowardly and weak, and have so little faith, but Allah knows best about them.