Augustine of Hippo

Now in order to convey this truth the Lord acted prophetically. By this I mean that in reference to the fig tree, it was not his will merely to exhibit a miracle but rather through this sign to convey an intimation of that which was to come. He often taught and persuaded us by such means. So even when our wills resist, he persuades us and brings us to faith.We first ask how was it the tree's fault that it had no fruit? Even if it had no fruit in its proper season, its season of mature fruit, still the tree would bear no fault. …

Sermon 89.3-6 ↗

Jerome

And when the disciples saw it, they marveled, saying, 'How did the fig tree wither at once?' However, according to the letter, the Lord, who was to suffer among the peoples and bear the scandal of the cross, had to strengthen the hearts of his disciples with the anticipation of a sign. And the disciples were amazed, saying: How did it wither immediately? Therefore, by the same power, could the Savior also dry up his enemies, unless he had awaited their salvation through repentance.

Commentary on Matthew ↗

Thomas Aquinas

"And the disciples seeing it wondered." Here first the wonder is presented; secondly, the satisfaction of the wonder. He says "and the disciples seeing it wondered." Just as men wonder when they see a spirit that seems good, and it quickly withers, so they wondered how it dried up so quickly.

Commentary on Matthew ↗