The saints in the second letter were assumed to be less joyful than in the first letter. Under persecution they had become confused as to the rapture and the appearing. The heavenly side of their faith had become dim, although their faith itself was strong. They needed further instruction as to the day of the Lord. Their faith continued to grow, for which the apostle gave thanks to God, and they had continued as before, but their joy had weakened.
Since the saints were passing through much persecution they were not so firm in hope. Furthermore the enemy had brought false doctrine among them, turning their eyes away from the rapture and saying that the day of the Lord had come. Not being acquainted with the full truth yet, the enemy sought to fill their minds with fear and false teaching.
The apostle, however, began by setting forth the truth showing the end of the matter-how the saints will be resting while the Lord will pour out His fury upon an unsuspecting people among the Gentiles and Jews.
The entire heavenly company, composed of the Church, the Old Testament saints, and the martyrs, will be at this appearing and the Lord will be "admired in all them that believe." For the professing world who are without life it will be everlasting destruction, while for the saints Christ will be glorified in them. This will be the day of His appearing, of Armageddon, of the revelation of our Lord Jesus Christ. The apostle desired that the name of the Lord Jesus Christ be glorified in them and they in Him.
How could persecution be the day of the Lord, when the wicked had control? In that day, the day of the Lord, the Lord would have control, the enemy put down. The judgment would be on those who knew not God, and those who believed not the gospel.