Do Old Testament individual, family and social laws and guidance apply to Christians or did Jesus come to discard OT laws and guidance? If OT laws are to be ignored by Christians, does God/Jesus provide substitute laws in the New Testament texts? I.e., if God thought it important to provide laws (in addition to requiring certain beliefs) to guide people prior to the New Testament, why has He not deemed it important to either re-affirm these same laws in the New Testament, or provide substitute laws?

Most Christians believe (I think) that accepting Christ in their lives provides innate guidance on how to lead their lives virtuously, and this impacts the creating of virtuous family and social life.  The implicit problem is that individual understanding of what is 'virtuous' may vary significantly as it applies to organizing and governing society.  I am trying to understand why God/Jesus Christ would replace detailed written guidance with something open to individual understanding and interpretation.
"Do not think that I came to abolish the Law or the Prophets; I did
  not come to abolish                           but to fulfill. 18 For
  truly I say to you, until heaven and earth pass away, not the smallest
  letter or stroke shall pass from the Law until all is accomplished. 19
  Whoever then annuls one of the least of these commandments, and
  teaches others to do the same, shall be called least in the kingdom of
  heaven; but whoever keeps and teaches them, he shall be called great
  in the kingdom of heaven." Matthew 5: 17-19.


It is clear from the above verses that Jesus did not come to discard the Law, even though a lot of churches do preach that. However, us as Gentiles are not required to follow the Law since the Law was mainly given to the Israelites and those who attached themselves to Israel (i.e. either were their slaves, servants or those who converted to Judaism).

When God sent Jonah to Nineveh, he asked that they repent and that was that, he did not demand that they follow the Law of Moses.

Jesus does ask us to follow his commandments. So whatever he said to us in the Gospels is what we should follow. Whether that means following the Law of Moses or not is a different matter (I, for one, don't believe that the Law is discarded or any such thing, God and his people have a lot of love for the Law of Moses. I don't believe God just sent it to tell people that they can't follow God's commands, I believe the Law is good and that we should use it as a guidance even if we don't follow it as legally and morally binding).


  "He who has My commandments and keeps them is the one who loves Me" John 14:21


This is, of course, my opinion.