'Call' in the Bible

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

As the Scripture says in Hosea, "Those who are not my people I will call my people, and the one who was not loved I will call my loved one.

There is no difference between Jew and Greek, because they all have the same Lord, who gives richly to all who call on him.

How, then, can people call on someone they have not believed? And how can they believe in someone they have not heard about? And how can they hear without someone preaching?