EVERLASTING GOD, The years go by but You're unchanging.
In this fragile world, You are the only firm foundation.
Always loving, always true, Always merciful and good, so good. Yesterday, today and forever, You are the same, You never change.
An unseen, dependable, unmovable lump of concrete is not what @vickybeeching had in mind when she wrote the song about our firm foundation, but what do we mean when we use these words? The who is Jesus but is he just solid, reliable, unseen and just for getting us started with building? A concrete foundation on which I build 'my faith'...
He is the one who the writer to the Hebrews says is the same yesterday, today and forever (13:8). The whole letter is about Jesus, and is very concerned with his foreverness and some very specific senses in which he is brilliant. We open Hebrews with the Jesus vs. the angels celebrity death match. And we're likely to get to the end of chapter 1 and cry out, Jesus is greater than the angels 'woo-hoo... who cares'. But, turns out it's important. the angel delivered the law and when Israel disregarded that they died. Jesus is more important than the angels, drift from him and it's a fate worse than death. Pay more attention to the big man.
We go on, shaken and drawn to Jesus. He, greater than the angels, became less than them for a while - why? To taste death for us and be the wrath-bearer (chapter 2). In all this we find he is our high priest and apostle. He's the one who rules the house (and he's better than Moses). Ergo, pay attention to what he says - hold on to confessing Jesus and not hardening your heart, on a daily basis. In all this we begin to find that this great high priest, the Son, has done his work and gone in to his Father where he intercedes for us - and he is the one who can help us when we're tempted and offers his mercy in our time of need. His is the throne of grace. Far from being concrete, God's ultimate revelation is very much personal, involved and with us.
Then (chapter 5) we begin to be told that he's a Melchizedek-priest. Eh? The line is repeated a third time before we reach the end of chapter 6 (via those apparently scary warnings). The writer doesn't think they'll quit but wants them to grow up - which means holding on to Jesus and not shifting from him. There's already evidence in their lives of it - and why would they want to go elsewhere?
Chapter 7 is all about Melchizedek and begins to explain why the writer cares so much that Jesus is a priest of the order of Melchizedek (who makes a cameo in Genesis 14). The chapter is complex but 8:1 tells us what the point is. This is the kind of priest we have - sat in heaven, job done, completed - not just in the toy temple but in the real thing - and so 8:12 sin is properly dealt with. In all this the key is that he's an eternal priest - unlike the old toy priests he doesn't die and have to be replaced - he lives forever so his priesthood lasts forever. That's the kind of unchanging we're talking about - unfailing, unending, everlastingly for us.
He's the one who comes at the time of reformation and it's the shedding of his blood that deals with sin. By his blood we can be made perfect forever (10:14) not that we would ever have contributed to this, but the really good news is that he hasn't got anything more to do. We can have total full assurance and 10:19 come on in boldly to the presence of the Father where the Son is seated. Like the old heroes (ch11) we then ought to look to Jesus (12:2) considering him. We don't presume on his grace, or trust in our sorrow (like Esau - ch12) - it would be easy to do that, but it's unthinkable too.
Instead we come to Jesus, by his better blood that can and will never fail because his priesthood, in which he offered himself for us, is never going to fail or end. It's this Jesus who is yesterday, today and forever, the same. And it's true that he's our foundation, and it's true that you can't see him at the moment - but he's very much alive, and very much coming back - and in the meantime let us go to him who came to us, (ch13) outside the camp, bearing suffering on his behalf, not quitting on loving his people, and hanging on to the gospel word that Jesus blood never fails me. Not yesterday. Not today. Never.