Albert Barnes Commentary 1 Thessalonians 3:12

"and the Lord make you to increase and abound in love one toward another, and toward all men, even as we also [do] toward you;" — 1 Thessalonians 3:12 (ASV)

And the Lord make you increase and abound in love. Compare to 2 Corinthians 9:8.

The word "Lord" here probably refers to the Lord Jesus, as this is the name by which he is commonly designated in the New Testament. See Barnes on Acts 1:24.

If this is so, then this is a petition to the Lord Jesus as the fountain of all grace and goodness.