Live By Faith - Galatians 2:20

...the life I now live in the flesh I live by the faith of the Son of God.

This is the very essence of the life of a disciple. The entire quote is this (comments added):

I am crucified with Christ:(this is in similitude of baptism - immersion under the water represents death - death of the old man, the man of sin.) nevertheless I live; yet not I, but Christ liveth in me:(Paul now clarifies what he means by "Christ liveth 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.

I do not take this to mean that Christ literally lives inside me, but that the meaning refers to the light of truth or the light of Christ which penetrates all things. The faithful strive to live by that light. The faithful recognize the light and the workings of the Spirit.

Furthermore, the footnotes refer us to this: John 17:22 - Part of what Christ prayed to the Father in the great intercessory prayer.

And the glory which thou gavest me I have given them; that they may be one, even as we are one.

Note the reference to glory - the light of Christ - which was given by the Father is now given - to who? v. 8,9: "them which thou hast given me". Meaning those who received the words which Christ had received from the Father and "have known surely that I came out from thee, and they have believed that thou didst send me."

2 Corinthians 5:15-17:

...he died for all, that they which live should not henceforth live unto themselves, but unto him which died for them, and rose again. Wherefore henceforth know we no man after the flesh: yea, though we have known Christ after the flesh, yet now henceforth know we him no more. Therefore if any man be in Christ, he is a new creature:old things are passed away; behold, all things are become new.

So faith leads us away from seeking our own pursuits unto true devotion to Him. Baptism is the first step, but devotion takes a lifetime. Thus by being in the light of Christ, and further having companionship with the Holy Ghost we are unified with Him and the Father. Purity and truth permeate us, and we are one with His divine will and with Him. The light of Christ is real - those of faith seek to live by its truth.