As you come to him, the living Stone -- rejected by men but chosen by God and precious to him --There are two thoughts here.
Obviously, Peter is starting a comment about coming to Christ. Literally, going to him, but as he mentions this, and calls him "the Living Stone" it spurs Peter into another thought. It is a thought about the response to Jesus Christ. Men rejected Him. God chose Him and He is precious to God.
Peter is saying (I believe) that when you come to Christ you are doing something radically different than the majority of men. For the most part, the population rejects Christ, but when you come to Him you are falling on the side of God's response to Christ. Christ is chosen by you, and He is precious to you.