Q. The question I have is this ; “What is the Purpose of the Church Age when Gentiles will also be saved in the Tribulation ?”
A. Paul described the purpose of the Church in Ephesians 2 where he said God raised us up with Christ and seated us with Him in the heavenly realms in order that in the coming age He might show the incomparable riches of His Grace. (Ephes 2:6-7) He did this purely as an act of His love where the only thing required of us is faith (Ephes. 2:8-9). He took some from among the Jews and some from among the Gentiles and in the process created a new race of mankind (Ephes 2:15). All who are saved between Pentecost and the Rapture belong to this new race.
Some were saved before the Church was born and others will be saved afterward. But none of them will have the exalted position or enjoy the level of blessing reserved for us. Only the Church has been adopted into the Royal Family of God, to share in His inheritance, and rule and reign with Him.