For yourselves know (αυτο γαρ οιδατε). This explanatory γαρ takes up in verses 1 Thessalonians 2:1-12 the allusion in 1 Thessalonians 1:9 about the "report" concerning the entrance (εισοδον, way in, εισ, οδον),

unto you (την προς υμας). Note repeated article to sharpen the point. This proleptic accusative is common enough. It is expanded by the epexegetic use of the οτ clause

that it hath not been found vain (οτ ου κενη γεγονεν). Literally,

that it has not become empty . Second perfect active (completed state) of γινομα. Every pastor watches wistfully to see what will be the outcome of his work. Bengel says: Non inanis, sed plena virtutis. Cf. 1 Thessalonians 1:5. Κενος is hollow, empty, while ματαιος is fruitless, ineffective. In 1 Corinthians 15:14; 1 Corinthians 15:17 Paul speaks of κενον το κηρυγμα ( empty the preaching ) and ματαια η πιστις ( vain the faith ). One easily leads to the other.