how is a man made righteous?

5 And he brought him forth abroad, and said, Look now toward heaven, and tell the stars, if thou be able to number them: and he said unto him, So shall thy seed be.

6 And he believed in the Lord; and he counted it to him for righteousness.


How did believing God that He would give him numberless descendants, account Abram righteous? Don't you have to believe in Jesus, not just a promise of blessing?

The man that trust God who justifies the wicked, his faith is credited as righteousness.