6 I marvel that you are turning away so soon from Him who called you in the grace of Christ, to a different gospel,
7 which is not another; but there are some who trouble you and want to pervert the gospel of Christ.
8 But even if we, or an angel from heaven, preach any other gospel to you than what we have preached to you, let him be accursed.
9 As we have said before, so now I say again, if anyone preaches any other gospel to you than what you have received, let him be accursed.
The Christ, Israel was waiting for
Luke 1:67 And his father Zacharias was filled with the Holy Ghost, and prophesied, saying, 68 Blessed be the Lord God of Israel; for he hath visited and redeemed his people, 69 And hath raised up an horn of salvation for us in the house of his servant David; 70 As he spake by the mouth of his holy prophets, which have been since the world began: 71 That we should be saved from our enemies, and from the hand of all that hate us; 72 To perform the mercy promised to our fathers, and to remember his holy covenant; 73 The oath which he sware to our father Abraham, 74 That he would grant unto us, that we being delivered out of the hand of our enemies might serve him without fear, 75 In holiness and righteousness before him, all the days of our life.
Content of Nathanael's belief
John 1:45 Philip findeth Nathanael, and saith unto him, We have found him, of whom Moses in the law, and the prophets, did write, Jesus of Nazareth, the son of Joseph. 46 And Nathanael said unto him, Can there any good thing come out of Nazareth? Philip saith unto him, Come and see. 47 Jesus saw Nathanael coming to him, and saith of him, Behold an Israelite indeed, in whom is no guile! 48 Nathanael saith unto him, Whence knowest thou me? Jesus answered and said unto him, Before that Philip called thee, when thou wast under the fig tree, I saw thee. 49 Nathanael answered and saith unto him, Rabbi, thou art the Son of God; thou art the King of Israel. 50 Jesus answered and said unto him, Because I said unto thee, I saw thee under the fig tree, believest thou? thou shalt see greater things than these.
What the Galatians had believed
Acts 2:22 Ye men of Israel, hear these words; Jesus of Nazareth, a man approved of God among you by miracles and wonders and signs, which God did by him in the midst of you, as ye yourselves also know: 24 Whom God hath raised up, having loosed the pains of death: because it was not possible that he should be holden of it. 25 For David speaketh concerning him, I foresaw the Lord always before my face, for he is on my right hand, that I should not be moved: 26 Therefore did my heart rejoice, and my tongue was glad; moreover also my flesh shall rest in hope: 27 Because thou wilt not leave my soul in hell, neither wilt thou suffer thine Holy One to see corruption. 30 Therefore being a prophet, and knowing that God had sworn with an oath to him, that of the fruit of his loins, according to the flesh, he would raise up Christ to sit on his throne; 31 He seeing this before spake of the resurrection of Christ, that his soul was not left in hell, neither his flesh did see corruption. 32 This Jesus hath God raised up, whereof we all are witnesses. 33 Therefore being by the right hand of God exalted, and having received of the Father the promise of the Holy Ghost, he hath shed forth this, which ye now see and hear. 36 Therefore let all the house of Israel know assuredly, that God hath made that same Jesus, whom ye have crucified, both Lord and Christ. 38 Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost. 39 For the promise is unto you, and to your children, and to all that are afar off, even as many as the Lord our God shall call. 41 Then they that gladly received his word were baptized: and the same day there were added unto them about three thousand souls.
Message of the gospel – Entire 1 Corinthians 15
1 Corinthians 15:1 - 58 Moreover, brethren, I declare unto you the gospel which I preached unto you, which also ye have received, and wherein ye stand; 2 By which also ye are saved, if ye keep in memory what I preached unto you, unless ye have believed in vain. 3 For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures; 4 And that he was buried, and that he rose again the third day according to the scriptures:
Christ had a kingdom
Ephesians 5:5 For this ye know, that no whoremonger, nor unclean person, nor covetous man, who is an idolater, hath any inheritance in the kingdom of Christ and of God.
Revelation 20:6 Blessed and holy is he that hath part in the first resurrection: on such the second death hath no power, but they shall be priests of God and of Christ, and shall reign with him a thousand years.
Labour in the Lord
1 Cor 15:58 Therefore, my beloved brethren, be ye stedfast, unmoveable, always abounding in the work of the Lord, forasmuch as ye know that your labour is not in vain in the Lord.
False Brethren - Zeal without knowledge
Romans 10:1 Brethren, my heart's desire and prayer to God for Israel is, that they might be saved. 2 For I bear them record that they have a zeal of God, but not according to knowledge. 3 For they being ignorant of God's righteousness, and going about to establish their own righteousness, have not submitted themselves unto the righteousness of God. 4 For Christ is the end of the law for righteousness to every one that believeth. 5 For Moses describeth the righteousness which is of the law, That the man which doeth those things shall live by them.
Different gospel preached a different lifestyle
Galatians 2:20 I am crucified with Christ: nevertheless I live; yet not I, but Christ liveth in me: and the life which I now live in the flesh I live by the faith of the Son of God, who loved me, and gave himself for me. 21 I do not frustrate the grace of God: for if righteousness come by the law [lifestyle of the law], then Christ is dead in vain.
Accursed from Christ
Romans 9:3 For I could wish that myself were accursed from Christ for my brethren, my kinsmen according to the flesh: