Charles Ellicott Commentary 1 Thessalonians 3:10

"night and day praying exceedingly that we may see your face, and may perfect that which is lacking in your faith?" — 1 Thessalonians 3:10 (ASV)

See your face.—Seeing them by proxy might satisfy for a while, but not for long. This exceedingly persistent prayer is caused by the feeling that it was Satan’s hindrance (1 Thessalonians 2:18), not God’s will, which forbade the meeting. He would not have prayed in such a way to go into Bithynia (Acts 16:7), for the essence of prayer is to conform the will to God’s will.

That which is lacking in your faith.—Bishop Wordsworth points out the unflattering faithfulness of St. Paul’s dealing with his converts. What the deficiencies were is unknown, but they certainly include a lack of knowledge of the state of the dead and concerning the Advent.