It is God's will that we be thankful. Jesus Christ is the mediator and revealer of God's will, and even He is subject to it (Luke 22:42). It is the will of God that we be thankful in every condition, in adversity as well as prosperity (James 1:2-3, 12).
Martin G. Collins
It is God's will for us to be thankful because He knows that it is good for us to have an attitude of thankfulness towards Him. When we have a thankful attitude and an attitude of appreciation for Him and what He does for us, it does not leave much room for ingratitude in our lives.
In reading Psalm 8:3-6, we can see ourselves in perspective to God's creation:
When I consider Your heavens, the work of Your fingers, the moon and the stars, which You have ordained, what is man, that You are mindful of him, and the son of man that You visit him? For You have made him a little lower than the angels, and You have crowned him with glory and honor. You have made him to have dominion over the works of Your hands; You have put all things under his feet. . . .
God has given us—humanity—dominion over the things that He has created. And beyond that, out of all humanity, we have been given a tremendous responsibility to develop righteous character and have the potential of living eternally in His Kingdom. This thought alone should help us to be thankful each day.
Other Forerunner Commentary entries containing 1 Thessalonians 5:18: