Beware of refusing to hear the call of God. Everyone who is saved is called to testify to the fact of his salvation. That, however, is not the same as the call to preach, but is merely an illustration which can be used in preaching. In this verse, Paul was referring to the stinging pains produced in him by the compelling force of the call to preach the gospel. Never try to apply what Paul said regarding the call to preach to those souls who are being called to God for salvation. There is nothing easier than getting saved, because it is solely God’s sovereign work— “Look to Me, and be saved…”Isaiah 45:22 
Our Lord never requires the same conditions for discipleship that he requires for salvation. We are condemned to salvation through the Cross of Christ. But discipleship has an option with it— “If anyone…” Luke 14:26

Paul’s words have to do with our being made servants of Jesus Christ, and our permission is never asked as to what we will do or where we will go. God makes us as broken bread and poured-out wine to please Himself. To be “separated to the gospel” means being able to hear the call of God. Romans 1:1. Once someone begins to hear that call, a suffering worthy of the name of Christ is produced. Suddenly, every ambition, every desire of life, and every outlook is completely blotted out and extinguished. Only one thing remains— “…separated to the gospel…” Woe be to the soul who tries to head in any other direction once that call has come to him. The Bible Training College exists so that each of you may know whether or not God has a man or woman here who truly cares about proclaiming His gospel and to see if God grips you for this purpose. Beware of competing calls once the call of God grips you.