The Mosaic law of the Bible contains many commands which Christians do not follow. These are generally regarded as "Ceremonial Laws" which have no moral value in themselves (e.g. the ban on eating shellfish).
However, the Bible itself does not clearly distinguish between which laws are "ceremonial" and which are moral requirements. Christian interpretations do not seem to follow any clear guidelines either - why should the ban on homosexual acts because they are ritually unclean not be considered "Ceremonial" as other such laws are ? Why should the ban on charging interest on loans to Jews not be considered a moral law to be extended to all people - as the Church indeed did for some considerable time ?
But this is not a problem unique to the Bible. It is one that occurs in everyone's mind. Our moral intuitions do not manage to cleanly distinguish widely agreed moral rules from parochial cultural rules. To do that requires conscious examination of the situation - and a willingness to accept that our personal moralities may not be absolute.
This fact is a further blow against the idea that there is an absolute morality. Our intuitive ideas about morality are one of the major lines of argument allegedly supporting the idea of an absolute morality. The fact that these ideas can be clearly wrong (if often not to the person holding them !) seriously undercuts any such argument.