All your quote form Hebrews 9 does is to state that the sacrifice of the Cross was necessary for salvation. It does nothing to advance your apparent argument, that the teaching of Christ given His disciples prior to His death and resurrection are of no interest to us. In fact, thank you, this is the first time I encounter this particular Protestant exegesis, that simply ignores 90% of the Gospel. It is so good that added it to my collection, which you can view on my profile (scroll to the end).
One can argue what the cardinal sin of Ananias and Sapphira was. The fact that their lie was about withholding a part of the proceeds cannot be irrelevant. Surely if they secretly did some paid work over the weekend and added the wages to the proceeds of the sale, then such a lie would not be punished. But be it as it may, whatever their particular sin was, the episode shows that a committed Christian can subsequently lose his salvation.
I have not said that they are of no interest to us. But it is not doctrinally binding upon us because Jesus has not died yet.