﴿When﴾ is a circumstance. ﴿To establish the truth﴾ [Al-Anfal: 8] ﴿You were calling upon your Lord﴾ meaning: you were seeking the help of the Benefactor towards you. This is a substitute for: 'when He promises you.' It is from the clarification of their dislike for encountering the one with the thorns due to their intense fear, which necessitated their calling for help along with the revelation of the outcome that the good is in what they disliked. That it is the most rightful of the truth, and it establishes the religion and weakens the matter of the polytheists.

And when He, glorified and exalted is He, hastened the response, He indicated that by saying: ﴿So He responded﴾ meaning: He brought forth the response as one who is in great desire for it. ﴿To you﴾ with the utmost of what you desire to strengthen your hearts. ﴿That I﴾ meaning: by that I ﴿Am providing you﴾ meaning: I am bringing forth the support 'to you' meaning: with My support for you. And perhaps He transformed the expression to what is in the statement with His pronoun of greatness and blessing. ﴿With a thousand of the angels﴾ while they are ﴿Following behind﴾ meaning: following with their likes.