In the words of Kyabje Kalu Rinpoche from his book, Luminous Mind (p. 106):
“Buddha, Dharma and Sangha together make up the Three Jewels. To take refuge in the Buddha, the Dharma, and those who practice and transmit it–the Sangha–is the first spiritual vow given on the basis of the faith that disposes us toward the Three Jewels and compels us to start our journey on this path.
“Taking refuge creates a spiritual connection that, on the one hand, protects us from the fears and anxieties we may have about suffering in samsaric or conditioned existence. It also protects us from obstacles in this life and in death, until we reach enlightenment. On the other hand, it leads and guides us toward enlightenment, showing us the path and guiding us along it. To take refuge until we reach enlightenment on behalf of all beings is to enter on the Buddhist path; it is the basis of Dharma.
“Taking refuge establishes a positive spiritual connection with the Three Jewels. It involves us in Dharma and practice but in no way implies that we reject or renounce faith we might have in other traditions. It is the basis for traveling the path to liberation; it protects us from what might make us turn away from that path, as well as from intentions and actions that would oppose it. When we truly take refuge, no obstacle can make us stumble; we will no longer be reborn in the three lower realms; and finally, because of our refuge vow, transmigration in the cycle of rebirths will eventually come to an end.”
From theVery Venerable Khenchen Thrangu Rinpoche, teaching on the Medicine Buddha practice:
“The function of taking refuge is to prevent your practice from becoming an incorrect path.
“The Three Jewels, which are the common sources of refuge [i.e., common to all traditions of Buddhism], are the Buddha, in whom one takes refuge by accepting him as a teacher and an example; the Dharma, in which one takes refuge by accepting it as a path; and the Sangha, in whom one takes refuge by accepting the Sangha as companions and guides on that path. Identifying the Three Jewels as the initial source of refuge indicates that by taking refuge in them you are freeing yourself from the possibility of an incorrect path.”
From Chogyam Trungpa Rinpoche, The Heart of the Buddha (page 85):
“In the Buddhist tradition, the purpose of taking refuge is to awaken from confusion and associate oneself with wakefulness. Taking refuge is a matter of commitment and acceptance and, at the same time, of openness and freedom. By taking the refuge vow we commit ourselves to freedom.”