Galatians 3:1-4 (ESV)
O foolish Galatians! Who has bewitched you? It was before your eyes that Jesus Christ was publicly portrayed as crucified.  Let me ask you only this: Did you receive the Spirit by works of the law or by hearing with faith?  Are you so foolish? Having begun by the Spirit, are you now being perfected by the flesh?  Did you suffer so many things in vain—if indeed it was in vain?
Paul wrote some Christians in a group of churches a letter that we now call Galatians. The reason he wrote them was because he had heard that those churches were giving in to some horrifying teaching. The teaching was that the work of Christ was insufficient to save people. In order to be saved, the false teachers were saying, one not only had to believe in Jesus, but one had to keep the Old Testament Law.
Paul uses very blunt language in his attempt to persuade the Galatian Christians to stick to the Gospel that he had preached to them – faith alone in Christ alone. In chapter 3 he continues to berate the Galatian Christians with arguments that they know the answer to and which show the foolishness of what they are doing in succumbing to the temptations presented to them.
Verse 4 – These people had actually suffered for the true Gospel and now they are willing to abandon it. This would make the suffering vain. No suffering truly done for Christ, for the one Gospel that is, is ever useless. But to suffer for something and then give up on it makes the suffering completely so.
A believer who suffers for the Truth and then decides that it isn’t the truth after all can look forward to nothing in terms of reward from God. The Christian life is not for the faint of heart. It demands much from us and if we are not willing to endure for the sake of Christ it is because we have never really put our faith in Him in the first place. We would be no more than the false conversions articulated in the parable of the sower
As for what was sown on rocky ground, this is the one who hears the word and immediately receives it with joy,  yet he has no root in himself, but endures for a while, and when tribulation or persecution arises on account of the word, immediately he falls away.  As for what was sown among thorns, this is the one who hears the word, but the cares of the world and the deceitfulness of riches choke the word, and it proves unfruitful.
Do not allow opposition to the Gospel cause you to surrender up your faith. God promises opposition to us and all who truly come to Him will suffer in some way. Salvation is for those who do not give up.
Matthew 24:13 – But the one who endures to the end will be saved.
Press on. Use all that God provides for your godliness (II Peter 1:3) and remember that the call of the Gospel is a call to die. Never, never, never, give up. It is the mark of true saving faith. Read I John 2:19 and show the genuineness of your faith. The rewards are out of this world.