There is this dispensational doctrine which I have addressed in other posts regarding the preaching of two different gospels, or a second way of salvation for the Jews. That way it is claimed is the Gospel of the kingdom which is stated to have been taught by Jesus and the disciples up until the choosing of Paul at which time the Gospel was changed from this kingdom gospel to the Gospel of Grace which Paul taught. Then once the pre-Trib Rapture occurs things somehow revert back to that gospel of the kingdom. What does scripture reveal about all this?

Speaking of Jesus in Acts 1:3 it is written:

To these He also presented Himself alive after His suffering, by many convincing proofs, appearing to them over a period of forty days and speaking of the things concerning the kingdom of God.

So yes Jesus taught the coming kingdom. Then Speaking of Paul in Acts 19:8 we hear: And he entered the synagogue and continued speaking out boldly for three months, reasoning and persuading them about the kingdom of God.

But Paul is also speaking of the kingdom. Again Paul is Speaking in Acts 20:25-27: And now, behold, I know that ye all, among whom I have gone preaching the kingdom of God, shall see my face no more. Wherefore I take you to record this day, that I am pure from the blood of all men. For I have not shunned to declare unto you all the counsel of God.

So Paul obviously preached about the kingdom, and yet, in another instance before, and near the beginning of his ministry Paul along with others is speaking of the kingdom:

Acts 14:21-23 And when they had preached the gospel to that city, and had taught many, they returned again to Lystra, and to Iconium, and Antioch, Confirming the souls of the disciples, and exhorting them to continue in the faith, and that we must through much tribulation enter into the kingdom of God. And when they had ordained them elders in every church, and had prayed with fasting, they commended them to the Lord, on whom they believed.

We can see that the kingdom was definitely part of Pauls gospel

Then speaking of of Philip, Peter and John in Acts 8:5, 12, 14-17: Philip went down to the city of Samaria and began proclaiming Christ to them. But when they believed Philip preaching the good news about the kingdom of God and the name of Jesus Christ, they were being baptized, men and women alike. Now when the apostles in Jerusalem heard that Samaria had received the word of God, they sent them Peter and John, who came down and prayed for them that they might receive the Holy Spirit. For He had not yet fallen upon any of them; they had simply been baptized in the name of the Lord Jesus. Then they began laying their hands on them, and they were receiving the Holy Spirit.

Again, the kingdom, and Speaking of Paul in Acts 28:23: When they had set a day for Paul, they came to him at his lodging in large numbers; and he was explaining to them by solemnly testifying about the kingdom of God and trying to persuade them concerning Jesus, from both the Law of Moses and from the Prophets, from morning until evening.

But what about in Paul’s writings?

1 Corinthians 6:9 Or do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived; neither fornicators, nor idolaters, nor adulterers, nor effeminate, nor homosexuals,

Again in Paul’s writings:

1 Corinthians 15:50 Now I say this, brethren, that flesh and blood cannot inherit the kingdom of God; nor does the perishable inherit the imperishable.

Again in Colossians 1:13: For He rescued us from the domain of darkness, and transferred us to the kingdom of His beloved Son,

Colossians 4:11 and also Jesus who is called Justus; these are the only fellow workers for the kingdom of God who are from the circumcision, and they have proved to be an encouragement to me.

2 Thessalonians 1:5 This is a plain indication of God’s righteous judgment so that you will be considered worthy of the kingdom of God, for which indeed you are suffering.

2 Timothy 4:1-2 I solemnly charge you in the presence of God and of Christ Jesus, who is to judge the living and the dead, and by His appearing and His kingdom: preach the word; be ready in season and out of season; reprove, rebuke, exhort, with great patience and instruction.

And then the Unknown author in

Hebrews 12:28:Therefore, since we receive a kingdom which cannot be shaken, let us show gratitude, by which we may offer to God an acceptable service with reverence and awe;

In James teaching: James 2:5 Listen, my beloved brethren: did not God choose the poor of this world to be rich in faith and heirs of the kingdom which He promised to those who love Him?

James didn’t say which He promised to the Jews, but to those who love Him. Then Peter’s teaching:

2 Peter 1:10-11 Therefore, brethren, be all the more diligent to make certain about His calling and choosing you; for as long as you practice these things, you will never stumble; for in this way the entrance into the eternal kingdom of our Lord and Savior Jesus Christ will be abundantly supplied to you.

The one thing that is very clear in these verses is the fact that all the Apostles taught the kingdom as part of the gospel. In fact there is only one gospel, one savior, Jesus the Christ, and He includes and promised to us the kingdom. It is promised to us and to all who are God’s children.