By contrast Christ’s ministry is far more excellent, it far surpasses the ministry of the Aaronic priests who dealt only with types and shadows, and furthermore it belongs to a better covenant, the covenant of grace, founded on better promises, the promises made to Abraham. They had an altar, but they didn't have the cross, the true atonement.
Why do we say that the covenant made with Moses was a covenant of works? The Bible tells us that on Sinai, because of sin, God restated, re-expressed that old broken covenant of the Garden of Eden, and in a sense he brought it back. [Many Christian teachers do not look at it in this way, but this is how our particular Baptist and independent traditions see it.] The covenant of works was given again on Mount Sinai to Moses: ‘Do this and live.’ Why would God reiterate that broken covenant? Because even though it was hopeless as a means of salvation – man had already failed to keep the condition of obedience – yet it was still in force in condemning the human race. Israel needed to be reminded that if they would not trust in the promises given to Abraham, then there was no alternative but to remain under the covenant of works, which could only condemn them. They had to understand that being the descendants of Abraham did not benefit them in any way as long as they failed to exercise faith. The same is true of all men and women. Therefore, to make this very clear, Sinai spelled out the Ten Commandments. It acted as a schoolmaster to drive us to Christ. People should have said, ‘These commandments, I do not keep them. I need the mercy and the help of God; I cannot earn or deserve God’s favour.’ Without the law we do not know what sin is. So the law was given as though God was saying to the Jews first and to all humanity, ‘If you will not have mercy, if you will not have grace, if you will not repent of your sin and have a free salvation, then you must face the full rigour of the law.’ So God brought back works, not because it can save us, but to humble us, and to show us our need of grace. In particular he did so with the Jews, to emphasise that although God had made a covenant with Abraham, as his physical descendants they only benefited from the physical side of that covenant – the land promises and so on – but they had no part in the spiritual side of the covenant unless they believed as Abraham believed. Until they exercised faith they remained under the law, the covenant of works, in spite of their physical ancestor.