St. Paul writes to the Ephesians and tells them that a mystery previously unknown but revealed to the Apsotles was that God desired and predestined  from the beginning to have a people for Himself, a family with which to share His love and glory. 

This He did by creating them free to choose Him and love Him, but as we learned, we often do not do that so His Son, the 2nd Person of the Trinity willingly died and was raised to life to reconcile us back to God, so that all who believe and are baptized might be part of this multinational, multiethnic people we call catholica ecclesia, or the "Catholic Church."