Charles Ellicott Commentary 1 Thessalonians 2:9

"For ye remember, brethren, our labor and travail: working night and day, that we might not burden any of you, we preached unto you the gospel of God." — 1 Thessalonians 2:9 (ASV)

For.—As in 1 Thessalonians 2:1, the general principles of the previous verses are supported by facts that the Thessalonians will remember. If this word 'For' connects to any particular phrase, it is to “impart our own souls,” and “we were ready to die for you; indeed, you remember how we worked ourselves almost to death.”

Labour and travail—These are not mere synonyms here: the first describes the kind of work; the second, its intensity: “our manual labour, and how hard we worked at that.”