9For you remember, brothers, our labor and toil: we worked night and day, that we might not be a burden to any of you, while we proclaimed to you the gospel of God.
This verse is introduced by the conjunction for, thus indicating that it explains something that has come before. In particular, it provides an explanation of what it meant for Paul to share his life with the Thessalonians.
9 For you remember, brothers, our labor and toil: we worked night and day, that we might not be a burden to any of you, while we proclaimed to you the gospel of God.