Matthew Henry Commentary Acts 10:9-18

"Now on the morrow, as they were on their journey, and drew nigh unto the city, Peter went up upon the housetop to pray, about the sixth hour: and he became hungry, and desired to eat: but while they made ready, he fell into a trance; and he beholdeth the heaven opened, and a certain vessel descending, as it were a great sheet, let down by four corners upon the earth: wherein were all manner of fourfooted beasts and creeping things of the earth and birds of the heaven. And there came a voice to him, Rise, Peter; kill and eat. But Peter said, Not so, Lord; for I have never eaten anything that is common and unclean. And a voice [came] unto him again the second time, What God hath cleansed, make not thou common. And this was done thrice: and straightway the vessel was received up into heaven. 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, and called and asked whether Simon, who was surnamed Peter, were lodging there." — Acts 10:9-18 (ASV)

The prejudices of Peter against the Gentiles would have prevented his going to Cornelius, unless the Lord had prepared him for this service. To tell a Jew that God had directed those animals to be considered clean which were previously considered unclean, was in effect saying that the law of Moses was done away. Peter was soon brought to understand its meaning. God knows what services are before us and how to prepare us; and we understand the meaning of what he has taught us when we find we need to use it.