For the law having a shadow of good things to come, and not the very image of the things, can never with those sacrifices which they offered year by year continually make the comers thereunto perfect. (Heb 10:1)
If you were standing outside next to a friend on a sunny day and their shadow was being cast on the sidewalk beneath you, would you carry on a relationship with their shadow? Nope. Why? Their shadow is a true representation of them, isn’t it? It is actually only there because they are there. So what is the problem? Well, the shadow isn’t alive. It isn’t the person themselves. You cannot know a shadow or have a relationship with them.
When it comes to Jesus Christ, His shadow cannot give YOU life.
The Old Covenant was a shadow of Christ. It truthfully represented Him. But it was not alive. Under the OT, His Spirit could be WITH people. But His Spirit could not be IN people.
The New Covenant is not the shadow, but the reality of Christ Himself — indeed, the New Covenant is CHRIST IN US. This is why, all through the NT, we are told that to try to live under the law is actually death – Christ will be of no effect to us – it will be as if He isn’t even in us. It will be like trying to live in a relationship with the shadow of Christ. Christ is not a shadow. Christ is certainly the Living embodiment of all that was in the OT — but far more — Jesus Christ is THE LIFE Himself — He is our life. The New Covenant is Christ in us.