Question: What is meant by “the day of God,” “the day of Christ,” and “the day of the Lord.?” S. T. G.
Answer: The context in each passage helps us to know its meaning. “The day of God,” is found in 2 Peter 3:12, 13. It is past all dispensations—the eternal day—when everything that can be shaken has passed away, and nothing remains but the new heavens and the new earth wherein dwelleth righteousness. And the lake of fire wherein all unrighteousness of men and angels finds its eternal judgment. (Rev. 21:1,8).
“The day of Christ,” or “Jesus Christ,” or “Lord Jesus Christ,” (Phil. 1:6,10; 2:16; 1 Cor. 1:8; 2 Cor. 1:14), point to the time when the Lord Jesus, having called us to meet Him in the air, will have His full delight in all His glorified saints, when as to them, “He shall see of the travail of His soul and shall be satisfied.”
“The day of the Lord,” (1 Thess. 5:2; 2 Peter 3:10; 2 Thess. 2:2 should read “the day of the Lord,” instead of “the day of Christ,” see New Translation), is when He comes with His saints to judge and reign and fulfill all the prophecies. And this day will extend from then over the Millennial Kingdom, and include the judgment of the dead at the great white throne. (2 Tim. 4:1).
See Volume I of “The Young Christian,” page 167 for answer to your question on the difference of “the Kingdom of heaven” and “of God.”