…so that being justified by His grace we would be made heirs according to the hope of eternal life.
By grace (receiving what we did not deserve through faith in Christ) we have been declared righteous (justified), and made heirs. Having been made righteous, we are His children and therefore we now have a right to all that Christ has provided for us. When someone passes away they have a will. That will determines who will receive what that person has given to them as a part of their inheritance.
Jesus having died for us provided to all who become a part of God’s family an inheritance. He wrote it in His will, the New Testament. If someone receives an inheritance from another person they have to claim that inheritance. So it is with what Christ has provided for us. He has given us in His will what we now have a right to, but we have to claim our inheritance.
You don’t earn an inheritance, it is yours because it was willed to you. In the same way we don’t earn the inheritance God has for us, it already belongs to us, but we claim it by faith in His written will. Take time to read and meditate on His Word so you can know of all He has provided for you, and claim by faith what you as child of God now have a right to because you are an heir of God.