Romans 4
19 And not being weak in faith, he did not consider his own body, already dead (since he was about a hundred years old), and the deadness of Sarah’s womb. 20 He did not waver at the promise of God through unbelief, but was strengthened in faith, giving glory to God, 21 and being fully convinced that what He had promised He was also able to perform. 22 And therefore “it was accounted to him for righteousness.”

It starts with knowing the plan of God for your life. Once you are confident in the plan, you hold on and never let go. Abraham knew what God had told him, so he believed.
As the scripture says, “and not being weak in faith.”

So this chapter is really focusing on salvation for all who believe and receive. It is not a part of the law. The law is separate. We receive this free gift of grace by only believing. There are no works we can do to earn it.