‘For you yourselves, brothers, know our entering into you, that it has not been found vain.'
This is his first evidence of his genuineness, the wonderful results that followed his ‘entering into' them. For the verb compare 1 Thessalonians 1:9. He had ‘come in' and the result had been the transformation of their lives (1 Thessalonians 1:9-10) as they well knew. Thus his visit had not been a failure, it had not been found empty and useless, accomplishing nothing. It had indeed accomplished a great deal.