He needed to change us from the heart out. The old covenant was a covenant with a nation. It was a covenant that expected the whole nation to work together to serve God. It was a representative covenant, so that the elders, the priests and the kings determined the spiritual state of the people under them. It meant that if one generation disobeyed, the following generation reaped the results.
Corporate responsibility is about to be replaced by individual accountability.
But that's because the means of obeying is going to change as well. God's plan is to bring his people back to life, to make it possible for us to respond in obedience to what's now written on our hearts. When I first studied computing at university we wrote our programs by hand, coded them onto cards and fed the cards into the computer, which would then carry out the instructions we'd worked out. It was a slow and laborious process to get the computer to do even a minor task. These days though I can sit down at my computer, open up a complex spreadsheet or database or word processing document and with relative ease do quite complex calculations.