A.T. Robertson Commentary Matthew 21:19

"And seeing a fig tree by the way side, he came to it, and found nothing thereon, but leaves only; and he saith unto it, Let there be no fruit from thee henceforward for ever. And immediately the fig tree withered away." — Matthew 21:19 (ASV)

A fig tree (συκην μιαν). "A single fig tree" (Margin of Rev. Version). But εις was often used = τις or like our indefinite article. See Mt 8:10; 26:69. The Greek has strictly no indefinite article as the Latin has no definite article.

Let there be no fruit from thee henceforward for ever (ου μηκετ σου καρπος γενητα εις τον αιωνα). Strictly speaking this is a prediction, not a prohibition or wish as in Mr 11:14 (optative φαγο). "On you no fruit shall ever grow again" (Weymouth). The double negative ου μη with the aorist subjunctive (or future indicative) is the strongest kind of negative prediction. It sometimes amounts to a prohibition like ου and the future indicative (Robertson, Grammar, pp. 926f.). The early figs start in spring before the leaves and develop after the leaves. The main fig crop was early autumn . There should have been figs on the tree with the crop of leaves. It was a vivid object lesson. Matthew does not distinguish between the two mornings as Mark does (Mr 11:13,20), but says "immediately" (παραχρημα) twice (21:19,20). This word is really παρα το χρημα like our "on the spot" (Thayer). It occurs in the papyri in monetary transactions for immediate cash payment.