John Calvin Commentary Acts 10:16

"And this was done thrice: and straightway the vessel was received up into heaven." — Acts 10:16 (ASV)

This was done thrice. The repetition of the vision served to confirm Peter, so that no doubt would remain in his mind. From this we gather how deeply the observance of the law was rooted in his mind. And I know no reason why God left him perplexed until the event that followed allowed him to learn the cause of the vision, except that, in his astonishment, he did not desire to know what this thing meant.

However, it was timely that the messengers of Cornelius came shortly afterward to interpret it. The vessel was finally taken up again into heaven, so that Peter might be assured that this message came from heaven, that is, from God.