What belongs to God versus what belongs to us according to Deuteronomy 29?

Les explains that secret things are matters nobody else knows anything about; they belong to the Lord our God. The things revealed, however, are made known by revelation to us and to our children forever, so that we may do all the words of the Law. Moses wrote under the Law, but he dealt with the same God we deal with, who has kept things secret until He saw fit to reveal it. Les connects this to Ephesians 1:9, where God made known the mystery or secret of His will according to His good pleasure purposed in Himself, because everything starts and finishes in the mind of God.