Now, to you and to me, the physical seems so solid. It is virtually indestructible. It is permanent - at least, in terms of own short existence on this earth. But this book (specifically, in relation to this sermon, the book of Hebrews) is telling us to get our attention off that which is immediate, that which is the around and the about, that which is so physically oriented to us. We are to get our lives, our thinking, our focus, out of that area and into the eternality of Christ's dominion.
One of the profound realities of God and His Word is that they are changeless. You remain, it says there, but we grow old, and we die. The eternal values never change, and even more exciting is that they can be taken through the grave.
Now, what in life is important to you? Is it the immediate gratifications that are offered by this world? Is it the around and the about? If so, I think it is not likely that you will see God very frequently.
Let us ask this question in another way. What is it that demands decisions and choices in your life? Brethren, we cannot identify with, we cannot worship, a transient process. Something must abide. That is what we are being told in verses 10-12. Something changeless must abide. Something must continue unchanging to which we may cling and within which we may live our life here by faith.