I read somewhere that Psalm 110 is the most-quoted passage in the New Testament. I don't know whether that's actually true, but it does seem to form the basis of our Christology. No, I don't mean everything we know about Christ is in Psalm 110 (we wouldn't need the gospels if it were), I mean that the New Testament authors quote Psalm 110 to show that God's plan with regard to Christ hasn't gone awry. The Lord Jesus Himself quotes Psalm 110 to show that He is David's Son as well as David's Lord, baffling both the Pharisees and the Sadducees (Matthew 22:41–46). Peter quotes the Psalm to show that Christ is now sitting at God's right hand (Acts 2:32–35). And, of course, Hebrews uses the Psalm to establish the connection between Christ and Melchizedek (Hebrews 5:6–10; Hebrews 7).
J. N. Darby's paper "The Melchisedec Priesthood of Christ" is well worth reading. It's been about twenty years since I first read that paper, but I remember being struck by the observation that Melchisedec – the first person the Scripture refers to as a priest – doesn't offer for sins.
J. G. Bellett wrote a book on Hebrews called, The Opened Heavens. I'm ashamed to admit I don't recall very much about that book, but the title is profound. The story of the golden calf at Sinai begins with the people getting tired of waiting for Moses (Exodus 32:1). He had gone up to speak with God, and they said, "we do not know what is become of him." We are very much in danger of saying the same thing: the Man who has delivered us has gone up into God's presence, and we have exactly the same tendency to get tired of waiting for Him to come back down (Acts 1:1–11). At the simplest level, Hebrews is written to tell us what's going on up there, where we can't see Him.
Darby links this current state of affairs with the Day of Atonement in Leviticus 16. We have a great High Priest who has passed into the heavens (Hebrews 4:14). Like the people of Aaron's day, we can't see what's going on with our Priest. What's He doing up there? The children of Israel might have wondered if Aaron had died when they couldn't see him (Leviticus 16:2, 13). We don't have that fear, but it does seem like He's been in there a long time...
Well, Hebrews tells us that He's in there for us (Hebrews 9:24). It's not that He got tired of us and left (although really, who could blame Him?), it's that He is appearing before the face of God for us.
What got me thinking about this was Exodus 28:29–30. Aaron was to have the names of the tribes of Israel over his heart whenever he went into the Tabernacle: " Aaron shall bear the names of the children of Israel in the breastplate of judgment on his heart, when he goes in to the sanctuary" (Exodus 28:29). He wasn't supposed to be able to forget that he was in there for them.
It's striking that Peter offered the return of Christ and the commencement of the Millennium if only the children of Israel would repent (Acts 3:19–21). I don't doubt that the Son of Man will come from Heaven to receive a kingdom (Daniel 7:13–14). Right now we're living in that intermediate period, where He is sitting at God's right hand, waiting for His enemies to be made His footstool. And there are deep and profound consequences of that.
But at the same time, He's now in Heaven for us. This is worth contemplating.