What may be called the inner or spiritual life of St. Paul may most of all be said to have been all Christ. His own theory of this innermost life is that it is a kind of living over again of the life of Christ: we die with Him to sin; we are buried with Him in baptism; as He rose, so we rise again to newness of life; He ascended to sit on the throne of the Father, and we are seated with Him in heavenly places. He is the very soil in which this life grows, and the atmosphere which it breathes; a Christian is "a man in Christ," and all the functions of his interior and even of his exterior life are performed in this element: he speaks in Christ, he marries in Christ, he dies in Christ, and in the resurrection he will rise in Christ.
This is what would be called the mysticism of St. Paul; and doctrines resembling this have sometimes been associated in religion with fantastic speculation and unpractical dreaming. In St. Paul, however, mysticism had no such results. If there was any part of his life on which the influence of Christ was more conspicuous than another, it was the practical part. To him any pretended connection or intercourse with Christ in secret had no meaning unless its outcome was visible in a Christlike life--"If any man have not the spirit of Christ, he is none of His."
To his own person he applied this principle in the most rigorous manner. Christ, he is fond of saying, lives in him; he almost speaks as if in his flesh the Son of God had experienced a second incarnation; but he relentlessly draws the practical conclusion. When Christ lived in His own earthly tabernacle, what did He live for? It was for the salvation of men; He went about continually doing good; He lived to seek and save the lost. If so, then, living in St. Paul, He must have the same purpose--to make use of his powers of mind and body for the salvation of the world. In this way Christ was really still carrying on the work which had been interrupted by His death. St. Paul dares to say that he is filling up that which was lacking of Christ's sufferings for the sake of His body, the Church. He says that the heart of Christ is yearning after men in his heart; that the mind of Christ is scheming for the kingdom of God in his brain; he even compares the marks of persecution on his body to the wounds of Christ.