Peter"s Jewish cultural prejudices were overriding the Word of God in his thinking. For this reason God repeated the vision two more times so Peter would be sure he understood God"s command correctly. [source][source][source]
"The threefold repetition might also remind Peter of an interview on a familiar beach [1]." [2][source]
"The message pervading the whole [3] ... is that the disciples are to receive the Gentiles, not before cleansing, but after God has cleansed them as He will do later through the cleansing Gospel which Peter will share with them the next day." [4][source]
"The particular application had to do with nullifying Jewish dietary laws for Christians in accord with Jesus" remarks on the subject in Mark 7:17-23. But Peter was soon to learn that the range of the vision"s message extended much more widely, touching directly on Jewish-Gentile relations as he had known them and on those relations in ways he could never have anticipated." [5][source]
I wonder if Peter remembered Jonah as he thought about the mission God had given him of preaching to the Gentiles. God had also called that prophet to carry a message of salvation to the Gentiles in Nineveh, but Jonah had fled from that very city, Joppa, to escape his calling. Now Peter found himself in the same position. [source][source][source]
"Because Jonah disobeyed God, the Lord sent a storm that caused the Gentile sailors to fear. Because Peter obeyed the Lord, God sent the "wind of the Spirit" to the Gentiles and they experienced great joy and peace." [6][source]