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When did Peter know Jesus was the Christ?
And Jesus answered and said unto him, Blessed art thou, Simon Barjona: for flesh and blood hath not revealed it unto thee, but my Father which is in heaven. - Matthew 16:17 (also Mark 8:29)
He first findeth his own brother Simon, and saith unto him, We have found the Messias, which is, being interpreted, the Christ. - John 1:41

A critic wants to know when it is that Peter figured out Jesus was the Christ. John 1:41 isn't a picture of Simon Peter figuring it out; it's a picture of Peter's brother Andrew figuring it out and telling Peter. What Peter figured out from that is not related -- but since this seems to be John's place for significant confessions (as Nathaniel's a few verses later) it seems likely that Peter had some doubts about Andrew's excitement, and didn't "get the point" at this time -- but did later, around when Matthew and Mark say he did.