Three times in Galatians 2:20, Paul uses the pronoun "in" (ἐν). Christ lives "in me" (ἐν ἐμοὶ). I live "in flesh" (ἐν σαρκί), and I live "in faith" (ἐν πίστει). The triple use of the pronoun "in" (ἐν) explains how we navigate the Christian life. There are three points on our navigation chart: Christ, flesh, and faith. The intersection of those three points determines how we live the Christian life.
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.
My life on earth is life in tension.
Christ lives in me, but I live in the flesh. Christ "in me" (ἐν ἐμοὶ) is a figurative expression for "the state of being filled with or gripped by something" or someone (BAGD, 259). Paul writes, "For in Him (ἐν αὐτῷ) all the fullness of deity lives in bodily form" (Col. 2:9). The fullness of all that God is fills, grips, and controls Christ. Christ lives in me in the sense that He fills, grips, and controls me. It is not His fullness that lives in me for I am not Christ (or God), but His person fills and grips my life for His purpose.
Yet I live in flesh (ἐν σαρκί). The word flesh here is not used in its ethical/theological sense, as in Romans 8:7-8. Here the word is physiological, referring to the mortal bodies our souls inhabit in our lives on earth. Flesh lacks the article indicating that we should understand it in qualitative terms. The pronoun "in" (ἐν) is locative, indicating the place in which we live, the sphere of physical life on earth. (BAGD, 258; Burton, Galatians, 138).
The tension is intentional and obvious. Paul rejects any notion that the divine life and our physical lives are "mutually exclusive," as some were teaching (Longenecker, Galatians, 93). Christ lives in me as I eat, drink, work, and play. He transforms our lives in the most elemental ways. Because Christ grips and controls me, He is there when I watch sports or movies. He enters the home with me. He interacts with co-workers through me. Christ is involved as I debate politics or argue about theology. Because Christ lives in me, even the most basic facets of life are filled with His transforming presence.
My life on earth is life in faith.
The expression "I live by faith (ἐν πίστει) in the Son of God" is placed in the clause so that the two prepositional phrases starting with "in" are next to each other for emphasis. Literally, it reads, "the life I now live in flesh, in faith, I live in the Son of God." The prepositional phrase can be either instrumental or locative, and there is a subtle but significant difference between the two. The New American Standard Bible translates it as instrumental "by faith." Faith is the means or instrument by which we live the Christian life (BAGD, 260). By faith becomes somewhat mechanistic. We are trusting Christ for the results in our lives. We achieve what we achieve by faith in the Son of God.
However, the two phrases "in flesh" and "in faith" are best taken as parallel constructions. Both "flesh" and "faith" are anarthrous, stressing the qualitative aspects of each. Both prepositions are best taken as locative, indicating the sphere in which we live. Just as it is not "by flesh" (the means), but "in flesh" (the sphere), so it is not "by faith" (the means), but "in faith" (the sphere) that we must live the Christian life (Meyer, Galatians, 93). Faith is the "atmosphere" in which we live and breathe (Lightfoot, Galatians, 119). The Son of God is the object of our faith. We think and act in the atmosphere of faith in the Son of God, who dominates our lives. We are not just trusting Christ for results. We are trusting Christ for life.
The Christian life involves total immersion in Christ, like a fish in the water. Our lives become autonomic, like breathing air as we live in an atmosphere of faith. In Physics, we achieve equilibrium when the elements exist in perfect balance. So too, in the Christian life, there is equilibrium in Christ. Like a marble at the bottom of a bowl, no matter how the bowl of life is turned, we are stable in the atmosphere of faith. In biology, there is homeostasis, the organism maintains a stable inner state despite outside changes. Like our bodily temperature regulates to remain stable, so faith in the Son of God regulates all of life so that we remain stable. Our awareness of Christ becomes so enveloping that we sense His presence in all we do and say.
Living in the atmosphere of faith in Christ is how we navigate our Christian lives.