I have been crucified with Christ; and it is no longer I who live, but Christ lives in me; and the life which I now live in the flesh I live by faith in the Son of God, who loved me and gave Himself up for me...
Galatians‬ ‭2:20
It is easy to believe that this is a theological statement; it is NOT. For a long time, I assumed, “Christ lives in me” is a theological statement — that it’s something I am supposed to just believe. While that may be true, that’s not what Paul is saying here in this passage. He is saying, practically, actually, Jesus Christ is the One living His life through Paul on a daily basis.  Theology has become testimony. The Word has “become flesh,” in Paul’s life.
I have had to learn the difference between good theology and a good testimony the hard way, over many years. I say I learned it the hard way especially because I held good theology, and for a long time, I thought that was enough. But good theology is not enough. If it’s difficult to appreciate the difference between theology and testimony, just examine your own life, as the Lord has led me to examine mine:
Is Jesus Christ the one yelling at other drivers?
Is Jesus Christ the one hedging the truth?
Is Jesus Christ the one pouting when He doesn’t get His way?
Is Jesus Christ the one getting frantic in traffic?
Is Jesus Christ the one admiring a pretty woman?
Is Jesus Christ the one indulging in gossipy conversation?
Is Jesus Christ the one fretting about how the bills get paid?
Is Jesus Christ the one hotly disputing with a neighbor?
Is Jesus Christ the one defending Himself against accusations?
No, that is not Christ in you and me. That is YOU in you. That is ME in me.
It is no longer I who live” was not merely Paul’s belief; it was the honest description of Paul’s daily life. He could confidently say, “That is Jesus speaking to my coworker,” “That is Jesus regarding this situation from a heavenly perspective,” “That is Jesus rejoicing in all circumstances,” etc. Jesus truly was able to manifest His life in the earthly life of Paul. It may be very different for you and me, but we can have great confidence that it is God’s desire for each of His children to move from a statement of belief to increasingly confessing the reality of Christ’s life within and through our lives. Praise God, the same Holy Spirit Who helped Paul victoriously live this life is available to us all in Christ, that the very same might be our testimony too.
But we have to clearly see that Christ will live in us only to the extent that we no longer live in us.
How To No Longer Live
What is the pathway to “no longer living”? It is by taking up the cross and nailing that old “I,” my self-life, to the cross every single day. “Now those who belong to Christ Jesus have crucified the flesh with its passions and desires” (Galatians‬ ‭5:24). ‬‬
This is not a one-time event, but a daily decision to walk the way that Jesus Himself walked, as He Himself said, “If anyone wishes to come after Me, he must deny himself, and take up his cross daily and follow Me” (Luke‬ ‭9:23‬). ‬‬
That’s what Paul meant when he said “I have been crucified with Christ” — that he had consistently obeyed Jesus’ command to deny himself and take up his own cross every single day. In another place, he says, “We are constantly being delivered over to death for Jesus’ sake, so that the life of Jesus also may be manifested in our mortal flesh” (2 Corinthians‬ ‭4:11‬). 
If we want Christ’s life manifested in our earthly lives, we must submit our selves (our flesh, our self-lives) to be delivered over to death constantly.
Daily taking up the cross, daily denying oneself, and daily crucifying the flesh with its passions and desires is what it means to “constantly be delivered over to death for Jesus’ sake,” and it is the only way to be able to humbly yet confidently proclaim, “It is no longer I who live, but Jesus Christ lives in me.”
We cannot produce the life of Christ; that is the work of God alone. We can only go down into death. And even the going down can only be accomplished by the help of the Holy Spirit: “...if by the Spirit you are putting to death the deeds of the body, you will live” (Romans‬ ‭8:13‬b). ‬‬
Ask the Holy Spirit to lead you in the way of the cross, to be your Helper in knowing how to crucify the flesh, and He will surely do it. Jesus longs to give the Helper He promised. “He is able to save to the uttermost — to the very last degree of difference between theology and testimony — those who draw near to God through Him” (Hebrews 7:25).
Praise God for the indescribable gift of Himself and His life is these earthen vessels. “He Who did not spare His Own Son, but delivered Him over for us, how will He not also with Him freely give us His nature too” (Romans 8:32 + 2 Peter 1:4).