I read this little article about someone trying to be more holy. OK, so kudos to them for wanting to be a better person, but I think there is a better way to look at the command to be holy (or as the blogger writes... BE HOLY).
I was reminded of a key aspect of the gospel stories; the redefinition of what holiness is. It's clear that the version of holiness in 2nd temple Judaism was one that encouraged people to avoid sin and uncleanness. Look through Leviticus for plenty of examples of "if you touch this unclean thing you shall become unclean." As a consequence, Jews wouldn't eat with Gentiles, for fear that the crockery wasn't clean according to Levitical standards. A husband couldn't touch his wife during her period for the same reason, nor could he touch the bed linen.
So the idea of holiness and uncleanness is one of contamination; that the holy can be contaminated by uncleanness.
Jesus makes the clear point that this is a false version of holiness. The holiness of God cannot be contaminated, it does the contaminating. The contact between the holy and the unclean does not make the holy unclean, it makes the unclean holy. In the gospels, when the sinner comes into contact with Jesus, they go away holy; when the diseased touch Jesus, they go away clean, etc.
Our contemporary concepts of holiness are caught up in the Levitical codes, making too many people think that to be holy (sorry... to BE HOLY) is to avoid doing sinful things and avoid sinful people. The appropriate Christian interpretation of the call to be holy is to redeem, rescue and forgive. Worrying about becoming unclean doesn't even enter into it. The concern is not about what to avoid, but about what to engage.