A.T. Robertson Commentary Galatians 5:18

"But if ye are led by the Spirit, ye are not under the law." — Galatians 5:18 (ASV)

Under the law (υπο νομον). Instead of "under the flesh" as one might expect. See Ga 3:2-6 for contrast between law and spirit. The flesh made the law weak (Romans 8:3; Hebrews 9:10,13). They are one and the same in result. See same idea in Ro 8:14. Note present tense of αγεσθε (if you are continually led by the Spirit). See verse 23.