He [Jesus] is the radiance of His [God's] glory and the exact representation of His nature, and upholds all things by the word of His power. When He [Jesus] had made purification of sins, He sat down at the right hand of the Majesty on high. Heb. 1:3, NASB.
So, we need to ask, where did Jesus go when He ascended?
Stephen answered that question in reporting the vision he received just before he became the first Christian martyr. In it he saw the risen Jesus in heaven at the right hand of God (Acts 7:56).
But it is the book of Hebrews more than any other in the Bible that describes where Jesus went and what He has been doing for the past 2,000 years. The opening verses tell us that after "He had made purification of sins, He sat down at the right hand of" God. And Hebrews 1:8 highlights both Jesus' divinity and His place on the throne. "But of the Son," we read, "Thy throne, O God, is for ever and ever, the righteous scepter is the scepter of thy kingdom" (RSV).
Today's passage has two important ideas, the first is that the divine Jesus did indeed take His seat on the governing throne of the universe in the place of honor at the right hand of the Father. In using that terminology the author of Hebrews is alluding to Psalm 110:1: "The Lord said to my lord: 'Sit at my right hand, till I make your enemies your footstool' " (RSV). That verse is the most cited Old Testament verse in the New Testament, and it undergirds much of the presentation in the entire book of Hebrews.
Of special interest in Hebrews 1:3 is that Jesus "sat down" at God's right hand. Earthly priests stood while performing their functions because they were continually offering sacrifices. But Jesus, who died "once for all" (Heb. 10:10, 14), had put an end to the need for any further sacrifice. His sacrificial work had been accomplished and never needs to be repeated. Thus the words "sat down" have an air of finality about them. Jesus "had made purification of sins." It was a completed work. He could now "sit down."
The Gospels highlight the great substitutionary sacrifice of Christ, "the Lamb of God, who takes away the sin of the world" (John 1:29, RSV). That part of Christ's work is over. He now moves on to the priestly aspect of His work, which is the focal point of the book of Hebrews. Another way of saying it is that in the Gospels Jesus accomplished our salvation, while in His heavenly priesthood He will apply the benefits of what He has done to each of His followers.