So if the Israelites obeyed the law in the OT, great things were promised them here on earth...and if we obey God after Calvary, great things are promised in heaven? The passage in Hebrews speaks of making those who approach, perfect. Not those who approach obeying for reward. I still don't see how you've addressed what the sacrifice itself actually did.
God gave the law and God gave grace, each in their due time, to suit His good pleasure. Each performed the function of His intent. If you have a problem with that you might should take it up with Him.