William Burkitt Anglican @expositoryburkitt

Here our apostle subjoins a reason, to enforce his foregoing exhortation; what he now required of them, was nothing but what at their first conversion to Christianity he had commanded them, and that in the name, and by the authority of Jesus Christ, to be performed by them; so that they were not his commands, but Christ's by him, and, as such, to be esteemed of them.

Matthew Henry Presbyterian @wholebiblehenry

Here we have, I. An exhortation to abound in holiness, to abound more and more in that which is good, Th1 4:1, Th1 4:2. We may observe, 1. The manner in which the exhortation is given - very affectionately. The apostle entreats them as brethren; he calls them so, and loved them as such.

Commenting on 1 Thessalonians 4:1-8

Jamieson-Fausset-Brown Reformed @jfbcommentary

by the Lord Jesus--by His authority and direction, not by our own. He uses the strong term, "commandments," in writing to this Church not long founded, knowing that they would take it in a right spirit, and feeling it desirable that they should understand he spake with divine authority. He seldom uses the term in writing subsequently, when his authority was established, to other churches.