Tafsir of Al-An'am 6:53

{And thus We have tried some of them} And like that great trial, We tested some people by means of others; meaning: We afflicted them with them. This is because the polytheists used to say regarding the Muslims: {Are these the ones whom Allah has favored from among us?}—meaning: favored with the success to attain the truth and with what He has prepared for them of happiness in His presence, to the exclusion of us, while we are the leaders and the elite, and they are the slaves and the poor. They said this in denial that the likes of them could be upon the truth or be the ones favored with goodness from among them. Similar to this is: {Has the message been sent down to him from among us?} (Al-Qamar: 25), and {If it had been good, they would not have preceded us to it} (Al-Ahqaf: 11).

The meaning of "We tried them" so that they would say this is: We abandoned them, so they were tempted/tested, until their temptation became the cause for this statement; for no one says the likes of their statement except one who is abandoned and tempted.

{Is not Allah most knowing of the grateful?} Meaning: Allah is more knowing of those from whom faith and gratitude proceed, so He grants them success for faith; and of those who persist in their disbelief, so He abandons them and denies them success.

{And when those who believe in Our verses come to you, say, "Peace be upon you. Your Lord has decreed upon Himself mercy: that any of you who does wrong out of ignorance and then repents after that and corrects himself, indeed, He is Forgiving and Merciful."}