In between first and second Thessalonians we read three Psalms and one chapter of Isaiah.
Psalm 98. Let us celebrate! Sing unto the LORD a new song!
Psalm 99. The LORD reigns. Exalt Him, He is holy.
Psalm 100. Six verses making a jubilant noise to the LORD.
Isaiah 59. We are hopelessly separated from God until we confess our sin, and even then we need a redeemer. He will come out of Zion.