John Calvin Commentary Acts 10:17

"Now while Peter was much perplexed in himself what the vision which he had seen might mean, behold, the men that were sent by Cornelius, having made inquiry for Simon`s house, stood before the gate," — Acts 10:17 (ASV)

Peter was taught not only by the vision but also by the Word of God; yet, in seeing, he did not see until the Spirit was an interpreter to him—a most excellent mirror of our own dullness. Although we are still very unlike Peter, for we are so far from readily understanding what God wills, or to what end He speaks to us, that many interpretations are scarcely sufficient for us.

But we must also note what Luke adds: that Peter thought earnestly upon the vision, that is, after he had recovered from his bewilderment. For this was a token of godly reverence, that he did not carelessly allow the vision to slip away. Therefore, the Lord opened to him when he knocked (Matthew 7:7).

And we are justly afflicted for our sluggishness, in that we benefit no better from the Word of the Lord, since we are so indifferent and have so little desire to inquire.