Acts 16:9

"And a vision appeared to Paul in the night; There stood a man of Macedonia, and prayed him, saying, Come over into Macedonia, and help us." Why a vision, and not the Holy Ghost? because He forbade the other. He would even in this way draw them over: since to the saints also He appeared in a dream, and in the beginning (Paul) himself saw a vision, "a man coming in and laying his hands upon him." In this manner also Christ appears to him, saying, "Thou must stand before Caesar." Then for this reason also He draws him thither, that the preaching may be extended. This is why he was forbidden to tarry long in the other cities, Christ urging him on. For these were to enjoy the benefit of John for a long time, and perhaps did not extremely need him (Paul), but thither he behooved to go. And now he crosses over and goes forth.

"And a vision appeared unto Paul in the night." Not now by Angels, as to Philip, as to Cornelius, but how? By a vision it is now shown to him: in more human sort, not now as before in more divine manner. For where the compliance is more easy, it is done in more human sort; but where great force was needed, there in more divine. For since he was but urged to preach, to this end it is shown him in a dream: but to forbear preaching, he could not readily endure: to this end the Holy Ghost reveals it to him. Thus also it was then with Peter, "Arise, go down." For of course the Holy Spirit did not work what was otherwise easy: but (here) even a dream sufficed him. And to Joseph also, as being readily moved to compliance, the appearance is in a dream, but to the rest in waking vision. Thus to Cornelius, and to Paul himself.