Walk. — Conduct yourselves: a metaphor very common in the writings of St. Paul, but not peculiar to them. It occurs three times in the Gospels, once in the Acts, thirty-three times in St. Paul’s Epistles, once in the Hebrews, ten times in the Epistles of St. John, and once in the Apocalypse.
In the Spirit. — Rather, by the Spirit — i.e. by the rule of the Spirit, as the Spirit directs. “The Spirit” is here undoubtedly the Holy Spirit — the Spirit of God, not the spirit in man.