Holiness is a lifestyle: not a title, not a religious affiliation, not a dress code. He has to make mention of weakness--as did Jesus--because we are human. As such, by our very nature, we have a propensity toward weakness. Though God is able to keep us from falling (Jude 24), the bible also says that we will not be tempted above that which we can bear and God will provide a way of escape (1 Cor 10:13).