John Gill Commentary Deuteronomy 27:26

"Cursed be he that confirmeth not the words of this law to do them. And all the people shall say, Amen." — Deuteronomy 27:26 (ASV)

Cursed [be] he that does not confirm [all] the words of this
law to do them
That is, who does not perfectly perform all that the law requires, and continues to do so; for the law requires obedience, and that perfect and constant, and in failure thereof curses, in proof of which the apostle produces this passage, (See Gill on Galatians 3:10), for the reconciliation of these Scriptures, as to what seeming difference there is between them; and all the people shall say, Amen; (See Gill on Deuteronomy 27:15); (See Gill on Deuteronomy 27:16).