Concerning “The Day of the Lord“; in Thessalonians, Paul compresses the details for the purpose of giving a summary statement concerning coming judgement. He highlights the point that on that first day when Christ returns there will be two immediate consequent effects.
The saints will be delivered – The Rapture
“For the Lord himself will descend from heaven with a cry of command, with the voice of an archangel, and with the sound of the trumpet of God. And the dead in Christ will rise first. Then we who are alive, who are left, will be caught up together with them in the clouds to meet the Lord in the air, and so we will always be with the Lord” 1 Thessalonians 4:16-17
and the wicked begin to be judged – Wrath of God
“when the Lord Jesus is revealed from heaven with his mighty angels in flaming fire, inflicting vengeance on those who do not know God and on those who do not obey the gospel of our Lord Jesus.” 2 Thessalonians 1:7
Paul is not intending to describe the full account of the complex-whole of judgement elements which we see in Revelation. He does however, give us hope that, in the end, God’s righteousness will prevail and he assures the Thessalonians that there will certainly be a coming day of retribution for their persecutors.