Christians and the Old Testament law

“For when there is a change of the priesthood, there must also be a change of the law.” Hebrews 7:12
Many Christians are confused about the role of the Old Testament law in their lives. On one extreme, are those who think everything in the Old Testament is irrelevant to us. But what of Matt. 5:17-18, where Jesus said, “Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfil them. I tell you the truth, until heaven and earth disappear, not the smallest letter, not the least stroke of a pen, will by any means disappear from the Law until everything is accomplished”? Then, on the other extreme, are those Christians who think they are justified by grace but sanctified by keeping the Law. They observe the Feasts and keep the Sabbath day in the same way as Jews do.
The writer to the Hebrews gives us an interesting and logical statement that helps to unravel this confusing issue. The Old Testament Law was associated with the Aaronic priesthood. But Jesus is of the priesthood of Melchizedek (Heb. 6:20, etc.). Therefore, it is not associated with the Old Testament Law. But this does not mean that we are without any law at all. During His ministry, Jesus did reiterate several Old Testament commandments for His disciples to follow (see Matt. 19:16-19). This is why many Christians feel obliged to keep the Ten Commandments, because of the similarity. However, although Jesus repeated some of the commandments, it is not the same law. Rather, we now have an even stricter law to live by: the law of love (Rom. 13:8-10, Gal. 5:14).