I assume that you are talking about what Paul says in Philippians, Chapter 3. There, he says that he has lost all things for the sake of knowing Jesus Christ. Therefore, his loss is completely associated with his acceptance of Christ because it is accepting Christ that made him lose everything.
In the earliest verses of this chapter, Paul establishes that he was a very important person among the Jews. He was a Pharisee, a member of the Jewish elite. This meant that he had a high position in society. But, in this letter, he is emphasizing that he has given away his position and his prestige. He has done this because he has come to realize that you do not gain salvation by following the law (by circumcising or anything else like that) but, rather, by knowing Jesus Christ.
Because Paul was a Pharisee and a member of the Jewish elite, he lost his position in society when he came to accept Jesus.