Under that covenant, God's people were not to intermingle with non-Jews, or Gentiles. God told them, "No Ammonite or Moabite shall enter the assembly of the Lord, and none of their decendents to the tenth generation." (Deuteronomy 23:3) The same was true of the illegitimate child. The "open lifestyles" of today have no place under the law of the Old Covenant. For this reason, many today are turning back to the law, hoping for a return from the godlessness of our age. But the law cannot make you righteous. It never could.
The Old Covenant and the New do not fit together. In seeking to mix them, you destroy the first and lose the second, just as Jesus explained with the new wine spilling out, destroying the old wine-skins. We cannot hack the law up into pieces (civil law, ceremonial law, criminal law, Levitical law, etc.) to fit it to our purposes. The man who chooses to live by the law must live by it all (Galatians 3:10). The New Covenant doesn't agree with the Law of Moses; it isn't supposed to. It is a better covenant, made on better promises.
The New Covenant is Christ, Himself, living in you and me. If the law keepers of His time hated Him, they will hate us also.