Extracted from the website of Buddhist Vajrayana Charity Funds Association and translated (三皈依的基本意義) into English:

The Fundamental Significance of the Three Refuges

The followings are the excerpt from Buddha Sutra:
◆	Take refuge in the Buddha for the rest of the life, from now on, regard the Buddha as Master, and will never take refuge in deviant demons and non-Buddhists. Take refuge in the Dharma for the rest of the life, from now on, regard the Dharma as Master, and will never take refuge in non-Buddhist books and scriptures. Take refuge in the Sangha for the rest of the life, from now on, regard the Sangha as Master, and will never take refuge in non-Buddhist evil masses.
◆	From now onwards, take refuge in the Buddha, take refuge in the Dharma, take refuge in the Sangha..
◆	Take refuge in the Buddha completely to the end, take refuge in the Dharma completely to the end, take refuge in the Sangha completely to the end.
According to the above sutra, we can understand that there are three levels within ‘The Three Refuges’ :
◆	The first level of refuge, is to take lifelong refuge in the Triple Jewels of the Buddha, the Dharma, the Sangha; lifelong is to begin from now on, in this lifetime, determine to take refuge in the Triple Jewels of the Buddha, the Dharma, the Sangha.
◆	The second level of refuge, is to take ultimate future refuge in Buddha, the Dharma, the Sangha; ultimate future is to begin from now on, no matter how many centuries, no matter how many millennia, to infinite lifetimes, take refuge in the Triple Jewels of the Buddha, the Dharma, the Sangha, until finally become a Buddha.
◆	The third level of refuge, is to take ultimate future refuge in Buddha completely to the end, take refuge in Dharma completely to the end, and take refuge in Sangha completely to the end. This is, to begin from now on, no matter how many Buddhas, I commit to take refuge to perfection; no matter how many Dharmas, I commit to take refuge to perfection; and no matter how many Sanghas, I commit to take refuge to perfection, until finally become a Buddha.