Paul is not saying that the Galatians’ suffering (or experience
in other translations) was in vain. Instead, he is warning them in order to provoke repentance. If they move from faith in Christ to faith in Christ and works of the law, then their faith is futile and they will not enjoy the salvation that Jesus brings. All their suffering (or experience) will have been for nothing.1
4 Avez-vous tant souffert en vain? si toutefois c'est en vain.