The Lord Jesus said during His earthly ministry that He was sent only to the lost sheep of the house of Israel.
Paul affirmed this:
Rom 15:8 Now I say that Jesus Christ was a minister of the circumcision for the truth of God, to confirm the promises made unto the fathers:
The Lord taught believers in Israel to pray, 'thy Kingdom come', because the Kingdom of Heaven is and always has been to natiional Israel according to prophecy and of course it will be on earth, with the twelve sitting on twelve thrones ruling over the twelve tribes of Israel and Messiah Jesus on David's throne.
After describing the ministry of the Lord Jesus to the circumcision, Paul then says this:
Rom 15:15 Nevertheless, brethren, I have written the more boldly unto you in some sort, as putting you in mind, because of the grace that is given to me of God,
Rom 15:16 That I should be the minister of Jesus Christ to the Gentiles, ministering the gospel of God, that the offering up of the Gentiles[natiions] might be acceptable, being sanctified by the Holy Ghost.
Rom 15:17 I have therefore whereof I may glory through Jesus Christ in those things which pertain to God.
Rom 15:18 For I will not dare to speak of any of those things which Christ hath not wrought by me, to make the Gentiles obedient, by word and deed,
The red letters are Christ's ministry to the circumcision/Israel and is according to prophecy.
Paul's ministry, in lieu of Israel's rejection of the Kingdom, is to the natiions and is according to mystery[things hitherto unrevealed].
One of those mysteries is the change of our[those in the Body of Christ] physical form in the blink of an eye, and being gathered up by the Lord Himself to meet Him in the atmosphere.
The elect of Israel are gathered by angels at the Lord's second coming to earth.