Charles Ellicott Commentary 1 Thessalonians 1:5

"how that our gospel came not unto you in word only, but also in power, and in the Holy Spirit, and [in] much assurance; even as ye know what manner of men we showed ourselves toward you for your sake." — 1 Thessalonians 1:5 (ASV)

“If God had not set His heart on you, we never could have been as successful among you as we were.”

Our gospel did not come to you.—Or rather, the good news we brought did not demonstrate its effect among you, in its impact on you.

In word only.—Compare 1 Corinthians 2:4; 1 Corinthians 4:20. “It did not consist merely of eloquent instruction, but we also found we were speaking with a conscious power—indeed with all the force of the Holy Spirit—and with an overwhelming conviction that we were right and would prevail.” That by “power,” “assurance,” etc., are meant things belonging to the preachers themselves, and not to the people, is proved by the next clause, “as you know.”

In the Holy Spirit.—The Greek here omits the definite article. In such cases, attention is not so much called to the Blessed Person Himself, as to the exalted, inspired enthusiasm with which He fills us. The union of the divine and human spirit is so close (see 1 Corinthians 6:17) that it is often difficult in the New Testament to distinguish which is meant.

As you know sums up with an appeal to their memory: “In fact, you recollect what God made us to be like among you.”

For your sake signifies not their own purpose, but God’s, carrying on the thought of the “election.”