Why did Peter think what God had cleansed would still be unclean,?Did he not get the message?
Peter's vision provided proof that God intended to make salvation available to all three groups of humanity; Jews, Samaritans, and Gentiles.
Cornelius and the others were not clean at the point of Peter's vision. That was accomplished after believing, receiving the Holy Ghost and obeying God's command of water baptism in the name of Jesus. This truth is revealed in verses 14-17. Verse 17 in particular speaks to Peter's command concerning water baptism. It was after God revealed His acceptance of the Gentiles by indwelling them that Peter commanded they be baptized in water. (Acts 10:43-48) According to Peter, if he neglected to do that he would be withstanding the purposes of God.
Acts 11:9-18
"But the voice answered me again from heaven, What God hath cleansed, that call not thou common.
10 And
this was done three times:
all were drawn up again into heaven.
11 And, behold, immediately there were three men already come unto the house where I was, sent from Caesarea unto me.
12 And the spirit bade me go with them, nothing doubting. Moreover these six brethren accompanied me, and we entered into the man's house:
13 And he shewed us how he had seen an angel in his house, which stood and said unto him, Send men to Joppa, and call for Simon, whose surname is Peter;
14
Who shall tell thee words, whereby thou and all thy house shall be saved.
15 And as I began to speak, the Holy Ghost fell on them, as on us at the beginning.
16 Then remembered I the word of the Lord, how that he said, John indeed baptized with water; but ye shall be baptized with the Holy Ghost.
17 Forasmuch then as God gave them the like gift as he did unto us, who believed on the Lord Jesus Christ; what was I, that I could withstand God?
18 When they heard these things, they held their peace, and glorified God, saying, Then hath God also to the Gentiles granted repentance unto life."