God’s rejection of Israel was never final, nor full. Indeed, God never fully rejects those whom He has promised to faithfully love. A remnant is always present and is much larger than we often perceive.
The most basic duty and greatest need for each believer is to consciously place our whole person under the Lordship of Jesus each day, including both the belief in our heart as well as the confession with our mouth.
Because Jesus is the end of the Law, He is the source of righteousness for all who believe in Him. God calls all men and women to confess with their mouth and believe in their heart that Jesus is Lord and Savior.