Second Temple Judaism often viewed holiness as a call to separation from secular society, because that was contaminated and unclean. However, in the life and teachings of Jesus, we see a dramatic shift in perspective regarding holiness. This is helpfully captured by Marcus Borg, in his brilliant book, Conflict, Holiness and Politics in the Teachings of Jesus.
In the teaching of Jesus, holiness, not uncleanness, was understood to be contagious. Holiness – the power of the holy, of the sacred – was understood as a transforming power, not as a power that needed protection through rigorous separation. Such is implied in the metaphor of the physician in Mark 2:17 par., set in the context of table fellowship. Physicians are not overcome by those who were ill, but rather overcome the illness.
Borg further notes that, "The viewpoint of the Jesus movement in Palestine is clear: holiness was understood to overpower uncleanness rather than the converse."
This understanding of holiness permeates early Christianity, and has its roots in the teachings of Jesus. As Borg further notes,
This prodigious modification of holiness in both Paul and the Palestinian church is best explicable as derivative from (and evidence for) the practice of Jesus. He implicitly modified the understanding of holiness. No longer was holiness understood to need protection, but as an active force which overcame uncleanness. The people of God had no need to worry about God’s holiness being contaminated. In any confrontation it would triumph.
Thus, when we study holiness in early Christian writings, we should be careful about what is determinative in our understanding - be it Philo, Qumran, the Pharisees, or other writers from Second Temple Judaism - because Jesus seems to have had the greatest impact on Christian conceptions of holiness.
 Marcus J. Borg, Conflict, Holiness and Politics in the Teachings of Jesus. (Harrisburg: Trinity International Press, 1998), 147.
 Borg, 149.