Oswald Chambers says, "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. 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."
Quoted
here.