The curtain in the tabernacle, and later the temple, seems to serve one important purpose according to the Scriptural testimony: it keeps sinful people away from God. That was both a burden and a blessing. A burden, because it cut human beings off from the fellowship with God for which they were designed; a blessing, because in fact in their sinful state human beings could not stand that fellowship. No one can see God and live.
I have been wondering whether there is something else going on here, as well as the obvious. The question 'where is God?' sounds, to us, hopelessly naive, but it was a question to which the OT Israelite would be able to give three answers. Firstly, God is in heaven, whence he does whatever pleases him. Secondly, God is throughout the world, directing and sustaining all creation. Thirdly, God is in the Most Holy Place, in the tabernacle/temple. These are all true, and some of the tensions between them are captured in Solomon's prayer of dedication at his great temple, recorded in 2 Chronicles 6. What strikes me, though, is that it is surely the third answer which gives the Israelite the greatest comfort, and upon which his faith rests. The fact that the OT often reports the perversion of this faith, portraying Israel as presuming upon God's favour because of his presence in the temple (see Jeremiah 7:4), merely reflects and underlines the fact that for Israel the presence of God in the temple is the foundation of their confidence.
Why is that? Why is the Lord's presence in the Most Holy Place more significant for Israel than his presence in the highest heaven?
I would suggest that it is only by taking up residence behind the curtain that God can be Israel's God, or rather that they can know him as Israel's God. The God of the heavens, and the God of the cosmos, are frankly not entities which can be known. Where is God? If not behind the curtain, if merely everywhere, what answer can we usefully give to the question? And doesn't the God who is not behind the curtain - not in a particular place - all to easily become the God who has no particular characteristics, and finally not a particular God at all but a vague and unknowable force? Whether we then go for pantheism, or prefer polytheism as a way of filling the gap between this unknown God and us, we certainly lose the real God, the personal God who is with us and for us.
Ironically, it seems that God has to curtain off a small section of the cosmos he has made in order to show himself as the Lord of the whole cosmos; ironically, in order to reveal himself as the God he really is, Yahweh must conceal himself behind a piece of cloth.
Consider, then, Hebrews 10:19-20: "...we have confidence to enter the holy places by the blood of Jesus, by the new and living way that he opened for us through the curtain, that is, through his flesh..."
Granted, the author of Hebrews has in mind primarily the curtain as the separation between holy God and sinful man - the more obviously Biblical application of the temple idea. But he does make the point that the tabernacle curtain was a sign of Jesus' human body - more than that, of his flesh, his whole human space-time existence. The particular God - the God who actually exists and is for us - takes flesh and hides himself in it so as to be revealed. God cannot be known in the abstract. He can only be known if we can give a satisfactory answer to the question 'where is God?'; and the answer we give is that God is in Christ.
In Hebrews, of course, the curtain is opened up. That, too, has happened. Christ's body, torn open on the cross, reveals God as he truly is - the crucified One, God in the depths, God suffering in my place. Is that, I wonder, why the veil of the temple was torn in two just as he died?
Irony: man in his sin hides from God, and is thus revealed to be the sinner he is; God in his righteousness hides himself from man, and is thus revealed to be the righteous God he truly is.
Implication: where do I look for God? Is it in his hidden-ness, or do I always clamour for the glory of the general God, the no-god?