Paul wrote this Second Letter to the Thessalonians to deny that he had written to the peoplee saying that the world was about to come to an end. He had wrongly been reported as saying, “The day of the Lord is at hand.”
The Responsorial Psalm matches Paul’s denial of that with the verse saying, “He has made the world firm, not to be moved.”
The universe is firm in that it is in God’s mage, as John wrote, “All things came to be through him, and without him nothing was made.”
O Lord my God, when I in awesome wonder
Consider all the worlds Thy hands have made
I see the stars, I hear the rolling thunder
Thy power throughout the universe displayed.