Deuteronomy - Chapter 27

This chapter ends with a series of curses.  the final one, in verse 26, says:

“Cursed is anyone who does not uphold the words of this law by carrying them out.”  Then all the people shall say, “Amen!”

This verse is quoted by Paul in Galatians 3, where he says that mankind is under this curse, because no-one completely follows all of God's laws:

"For as many as are of the works of the law are under the curse; for it is written, “Cursed is everyone who does not continue in all things which are written in the book of the law, to do them.” But that no one is justified by the law in the sight of God is evident, for “the just shall live by faith.” Yet the law is not of faith, but “the man who does them shall live by them.” Christ has redeemed us from the curse of the law, having become a curse for us (for it is written, “Cursed is everyone who hangs on a tree”), that the blessing of Abraham might come upon the Gentiles in Christ Jesus, that we might receive the promise of the Spirit through faith."