For. — As in 1 Thessalonians 2:1, the general principles of the foregoing verses are supported by facts which the Thessalonians will remember. If the word attaches itself to any particular phrase, it is to “impart our own souls,” “we were ready to die for you; indeed, you remember how we worked ourselves almost to death.”
Labour and travail — not mere synonyms here: the first describes the kind of work; the second, the intensity of it: “our manual labour, and how hard we worked at that.”