Our God is a God of covenant. By His name, Yahweh, He entered into covenant with the children of Israel.
The book of Deuteronomy is the document of that covenant. Chapter 28 gives a series of blessings and curses. If His people obeyed His voice and kept His commandments, they would experience the His blessings.
If His people chose not to hear His voice or obey His commands, the would not experience His blessings. Outside the blessing, there is not left but the curse.
Sin, sickness and disease belonged to the curse. This requires a choice on the part of people. It is the covenant made with Moses.
A New and better Covenant is fulfilled in the Lord Jesus Christ.
He redeemed us from the curses of the old covenant by becoming a curse for us. He redeemed us from the curse of the Law, having become a curse for us, that the blessing of Abraham might come upon the Gentiles in Christ Jesus Galatians 3:13,14.