Gr. epithumia, “lust” (see on Mark 4:19). For comment on the expression “lust of the flesh” see on Rom. 13:14. To “fulfil the lust of the flesh” is to accept the guidance of carnal passions, feelings, and desires, the antithesis of walking “in the Spirit.” The way of the Spirit leads to life, but the way of the flesh leads to death (see Rom. 8:6-8). The word “flesh” here stands for the corrupt human nature.

 Literally, “walk in Spirit,” that is, in harmony with spiritual ideals (see on Rom. 8:1, 14). Paul uses this expression repeatedly in his epistles. The Holy Spirit is God’s appointed agent to lead men to eternal life (see on John 16:8-11).