"To him that overcometh will I grant to sit with me in my throne, even as I also overcame, and am set down with my Father in his throne." (Revelation 3: 21)
When reading the final book of the New Testament, we have to keep in mind that Jesus is the same yesterday, today, and forever (Hebrews 13: 8), and that He is Him who has been from the beginning (1 John 2: 12-14)
The revelation of all that Jesus has done for us at the Cross cannot be diminished, for Jesus announces who He is based on what He did for us:
"I am Alpha and Omega, the beginning and the ending, saith the Lord, which is, and which was, and which is to come, the Almighty." (Revelation 1: 8)
"I am he that liveth, and was dead; and, behold, I am alive for evermore, Amen; and have the keys of hell and of death." (Revelation 1: 18)
When Jesus states "He that overcomes", many think "What must I do to overcome, so that He will set me on His throne with Him?"
In that verse, Jesus is addressing one of the back-slidden churches:
"Behold, I stand at the door, and knock: if any man hear my voice, and open the door, I will come in to him, and will sup with him, and he with me." (Revelation 3: 20)
Obviously, Jesus is not addressing those who believe on Him already, since He speaks to "any man".
What about those who believe on Him already? Paul informs us:
"37Nay, in all these things we are more than conquerors through him that loved us. 38For I am persuaded, that neither death, nor life, nor angels, nor principalities, nor powers, nor things present, nor things to come, 39Nor height, nor depth, nor any other creature, shall be able to separate us from the love of God, which is in Christ Jesus our Lord." (Romans 8: 37-39)
We are more than conquerors, or literally "hyper victors" in the original Greek.
We are also already seated with Christ:
"But God, who is rich in mercy, for his great love wherewith he loved us, 5Even when we were dead in sins, hath quickened us together with Christ, (by grace ye are saved;) 6And hath raised us up together, and made us sit together in heavenly places in Christ Jesus: " (Ephesians 2: 4-6)
While Jesus speaks of those who overcome in Revelation, we must rest assured that for us who believe on Jesus, we are already more than overcomers and seated with Him!