'Rely' in the Bible

Now if you call yourself a Jew, and rely on the Law, and boast about God,

but for our sake also—to whom righteousness will be credited, as those who believe in Him who raised Jesus our Lord from the dead—

because if you acknowledge and confess with your mouth that Jesus is Lord [recognizing His power, authority, and majesty as God], and believe in your heart that God raised Him from the dead, you will be saved.

But how will people call on Him in whom they have not believed? And how will they believe in Him of whom they have not heard? And how will they hear without a preacher (messenger)?