Romans 4:2, 13-15

Was it by his good works of keeping the law? No. For if it was by the things he did, he would have something to boast about, but no one boasts before God.

God promised Abraham and his descendants that they would have an heir who would reign over the world. This royal promise was not fulfilled because Abraham kept all the law, but through the righteousness that was transferred by faith. For if keeping the law earns the inheritance, then faith is robbed of its power and the promise becomes useless. For the law provokes punishment, and where no law exists there cannot be a violation of the law.