Theophylact of Ohrid

Do you see? Everywhere our action comes first, and then God's cooperation follows. For God cooperates with us when we act and make a beginning, but when we do not act, He does not cooperate. Notice also that deeds follow words and the word is confirmed by deeds, just as with the apostles the word was confirmed by the deeds and signs that followed. …

Commentary on Mark ↗

Augustine of Hippo

It goes on: And they went forth and preached every where, the Lord working with than, and confirming the word with signs and wonders. (Epist. cxcix. 12.) (Acts 1:8) But how was this preaching fulfilled by the Apostles, since there are many nations in which it has just begun, and others in which it has not yet begun to be fulfilled? …

Catena Aurea by Aquinas ↗

Gregory the Dialogist

"And they went forth and preached everywhere, the Lord working with them, and confirming the word with signs following." What is to be considered in these things, what is to be committed to memory, except that obedience followed the command, and signs indeed followed obedience?

Forty Gospel Homilies, Homily 29 ↗

Bede

But they, having departed, preached everywhere, with the Lord working with them and confirming the word with the accompanying signs. What is to be considered in this, what to be commended to memory, except that they followed the command with obedience, and obedience was followed by signs? Among these, it is notable that Mark, although he began his Gospel later than the others, extended it to longer times in his writing. …

On the Gospel of Mark ↗