Positively Moses taught that justification came by faith ( Deuteronomy 30:11-14). In the context of Moses" statement there is a strong emphasis on an attitude of loving obedience rather than a legalistic approach to earning righteousness ( Deuteronomy 30:6-10). Moses" point was that the Israelites should not think that pleasing God was something beyond their reach. A proper attitude of faith toward God is essentially what He required. [source][source][source]
In quoting this passage Paul made his own application of it in harmony with his argument. It was vain for the Israelites to think that they had to be good enough to ascend into heaven to bring the promised Messiah down to earth to save His people. Likewise it was foolish for them to think that they had to be good enough to raise Messiah up from the death that the prophets had predicted He would die. God had already done those things for the ungodly in the incarnation and resurrection of Jesus Christ. All they had to do was accept what God had done for them in Christ. [source][source][source]