Both the Old and the New Testament are filled with references to keeping the Commandments. Not to BE saved but because we ARE saved.
And said, I beseech thee, O LORD God of heaven, the great and terrible God, that keepeth covenant and mercy for them that love him and observe his commandments:
Nehemiah 1:5
Let us hear the conclusion of the whole matter: Fear God, and keep his commandments: for this is the whole duty of man.
Ecclesiastes 12:13,14
For God shall bring every work into judgment, with every secret thing, whether it be good, or whether it be evil.
This is the New Covenant by faith that we are to walk in:
Behold, the days come, saith the LORD, that I will make a new covenant with the house of Israel, and with the house of Judah.
Jeremiah 31:31,33
But this shall be the covenant that I will make with the house of Israel; After those days, saith the LORD, I will put my law in their inward parts, and write it in their hearts; and will be their God, and they shall be my people.