bible.com/bible/100/gal.5.16.NASB1995

Walk by the Spirit. All believers have the presence of the indwelling Holy Spirit (cf. Ro 8:9; 1Co 6:19, 20) as the personal power for living to please God. The form of the Gr. verb translated “walk” indicates continuous action, or a habitual lifestyle. Walking also implies progress; as a believer submits to the Spirit’s control—that is, responds in obedience to the simple commands of Scripture—he grows in his spiritual life (see notes on Ro 8:13; Eph 5:18; Col 3:16). the flesh. This is not simply the physical body, but includes the mind, will, and emotions which are all subject to sin. It refers in general to our unredeemed humanness. See notes on Ro 7:5; 8:23; cf. v. 13.

All credit to John MacArthur Study Bible.