WHY THIS?
The Old Testament contains reference to many laws that are not enforced today.
Does that mean Christians are in error not obeying them, or the Bible is no longer relevant, or something else?
"What about all those laws that were supposed to be binding for all time?"
RESPONSE:
This is going to depend on the particular laws in question.
Moral laws, with which you're probably most familiar, are still to be in force today. This is because they are characteristic of God himself. If they are characteristic of God, and God's character is eternally unchanging, then these laws should likewise be eternally unchanging.
Ceremonial laws largely prefigured God's redemptive work of the cross (like sacrifice). With the coming of Christ ("I did not come to abolish the Law but to fulfill it"), those laws were completed.
Dietary laws, similar to ceremonial ones, served perhaps two purposes. They served (primarily I think) to set Israel and Israelites apart from the rest of the world. These were, and to an extent still are, material examples of the spiritual sanctification God's people are to exhibit in the midst of an unbelieving world.
Dietary laws additionally (intentionally I believe) served to protect early people from certain nutritional dangers (bottom-feeding creatures, scavenger birds, etc.) which civilization would only later come to discover and eventually circumvent.
Social/civic laws were for the operation of the nation-state of Israel. If indeed these were to be binding for all time, "all time" likely ended along with the original nation-state in AD 70.
See also:
Did God give us laws we can't keep?
Principles of God's judgment
Expanded!