'Om Mani Padme Hum' (translation: 'Hail the jewel in the lotus') is a six syllable invocation (mantra) of Avlokitesvara, one who is invoked as the Protector from danger.
Does it mean protecting from danger as purifying :
I'm going to try to answer your question by equating "danger" with Mara (devils). Buddha used Mara both literally and figuratively, such as gods in heavens who hold wrong views, 5 skanda, attachment to sensual pleasures etc. He said meditation from 1 first Jhanna is a safe place to hide from those dangers.
However, if danger in a sense of things happen to you like car accident, danger from natural disaster, sickness, aging, and causes of death, nothing can help for those are the way it is and from Karma.
(imo) In that the phrase points to the Buddha and his message (convoluted though it may be for those not in the know!), whilst at the same time recognizing the terms for some of dangers present within experience, that the Buddha pointed to, there is both a 'carrot' and a 'stick' in this phrase, in regards to the path.
Since 'danger' is effectively based on Kamma coming to fruition - Kamma being conditioned by an individual's thoughts, words and actions - this phrase should incline the mind to avoid some negative kammic fruits, whilst influencing it to take up the Buddha and his message.
(I assume the 'jewel in the lotus' is the Buddha.. for this, the phrase deserves some caution, because the Buddha primarily wished his followers to follow his Dhamma - through personal insight, rather than substitute personal progress by placing him on a pedestal)
