For yourselves, brethren, know our entrance in unto you - notes, 1 Thessalonians 1:9. Paul appeals to themselves for proof that they had not come among them as impostors. They had had a full opportunity to see them, and to know what influenced them. Paul frequently appeals to his own life, and to what they, among whom he labored, knew of it, as a full refutation of the slanderous accusations of his enemies; compare notes, 1 Corinthians 4:10-16; 1 Corinthians 9:19-27; 2 Corinthians 6:3-10. Every minister of the gospel ought so to live as to be able, when slanderously attacked, to make such an appeal to his people.
That it was not in vain - κενὴ kenē This word means:
(1)Empty, vain, fruitless,” or without success;
(2)That in which there is no truth or reality - “false, fallacious;” Ephesians 5:6; Colossians 2:8.
Here it seems, from the connection 1 Thessalonians 2:3-5, to be used in the latter sense, as denoting that they were not deceivers. The object does not appear to be so much to show that their ministry was successful, as to meet a charge of their adversaries that they were impostors. Paul tells them that from their own observation they knew that this was not so.