"I have been crucified with Christ; 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 for me." (Galatians 2:20)
When Jesus died on the Cross, He knew that if we go to hear about His love, we'd believe and become one with Him. He had faith in what He did, in His vicarious sacrifice for us. He trusted that we'd become everything He died, was buried, and rose back to life for. That's the faith of the Son of God by which we're supposed to live.
Think about it this way: imagine you're son is about to take his SAT. That exam would cost you the rest of the money in your bank account, but you're willing to stake everything. You tell him, "Son, we're spending our last dollar on this test, but it's nothing, because we know you'll pass. When you do, things will change for this family."
Now, your son understands that his entire family is depending on him. He know's he's got to pass this test-- he can't afford to disappoint everyone. So, he'll act on YOUR faith in him, which will become his driving force. His friends may be out partying, but he'll act differently, because he knows you've invested everything in him, and he wants to justify your confidence in him.
That's like Galatians 2:20-- the life we live now, we live by the faith of the Son of God, who loved us and gave up everything for us. We can't fail or disappoint Him. This is the reason you must live your life differently. You must set your affection on Him, on things above, and not on things on the earth or the flesh. Be determined to walk in, and manifest, the full blessings of the Gospel that are yours in Christ. Live up to His dream, to His expectation. Live by the faith of the Son of God!
I was crucified with Christ, nevertheless I live; yet not I, but Christ lives in me, and the life which I now live in the flesh, I live by the faith of the Son of God who loved me, and gave Himself for me. My life is ever for His glory. Hallelujah!
Further Study: Colossians 3:1-3; Matthew 6:33; 1 John 2:15-17