وَإِن يُرِيدُواْ خِيَانَتَكَ فَقَدْ خَانُواْ اللّهَ مِن قَبْلُBut if they intend to betray you, they indeed betrayed Allah before,meaning, وَإِن يُرِيدُواْ خِيَانَتَكَ (But if they intend to betray you) in contradiction to what they declare to you by words. فَقَدْ خَانُواْ اللّهَ مِن قَبْلُ (they indeed betrayed Allah before), the battle of Badr by committing disbelief in Him,فَأَمْكَنَ مِنْهُمْSo He gave (you) power over them,causing them to be captured in Badr,وَاللّهُ عَلِيمٌ حَكِيمٌAnd Allah is All-Knower, All-Wise.He is Ever Aware of his actions and All-Wise in what He decides