Besides believing what God has revealed, what else must we do to be saved? Besides believing what God has revealed, we must keep His law.
If you love me, keep my commandments. (John 14:15)
Which are the two great commandments that contain the whole law of God? The two great commandments that contain the whole law of God are:
And one of them, a doctor of the Law, putting him to the test, asked him, "Master, which is the great commandment in the Law?" Jesus said to him, "'Thou shalt love the Lord thy God with thy whole heart, and with thy whole soul, and with thy whole mind.' This is the greatest and the first commandment. And the second is like it, 'Thou shalt love thy neighbor as thyself.' On these two commandments depend the whole Law and the Prophets." (Matthew 22:35-40)
Further reading: CCC 2052-2055