Yamas consist of AHIMSA (nonviolence), SATYA (truthfulness), ASTEYA (nonstealing), BRAHMACHARYA (chastity or celibacy), and APARIGRAHA (the nonreceiving of gifts).
Nonviolence: While many of these disciplines seem self-evident, some of them need further explanation. Serious spiritual aspirants, Swami Vivekananda said, "must not think of injuring anyone, by thought, word, or deed. Mercy shall not be for human beings alone, but shall go beyond, and embrace the whole world."
Truthfulness not only means speaking truthfully but also adhering to the truth in thought, word, and deed. Ramakrishna said that "making the heart and lips one" was the spiritual discipline of our age.
Nonstealing also means noncovetousness: it means not desiring things that belong to others and not appropriating what belongs to others. Even using someone else's words or ideas and presenting them as our own without acknowledging their source is a kind of stealing.
Chastity or celibacy is stressed for two reasons: First, serious spiritual seekers need to conserve the energy generally directed to sex and to redirect it to Self-realization. Second, physical or mental sexual activity reinforces our idea of ourselves as bodies and not as Spirit. If we want to progress in spiritual life, we need to regard other people as human beings—as manifestations of God—and not as male and female bodies.
We should add here that Vedanta is meant for all people—not simply those with monastic inclinations. Vedanta acknowledges that sexual desire is, at its core, longing for union with God. While strict celibacy is stressed for monastics, Vedanta advocates sexual responsibility and self-control for nonmonastics. For nonmonastics, chastity means fidelity to one's spouse. Further, when approached in the right spirit, marriage is a sacred spiritual path. One's spouse is also one's spiritual partner and should be looked upon as a manifestation of divinity.
Nonreceiving of gifts: The ethical virtues listed above may seem fairly reasonable, but what's the problem with accepting gifts? We can see from this guideline how carefully the ancient Hindu sages watched the workings of the mind. Accepting gifts from others makes us feel obligated: we can become manipulated through them and lose our independence. Sometimes gifts are really bribes in disguise: if we feel even vaguely indebted to the giver, our minds become tainted. Sometimes the effect is obvious, sometimes it is subtle; but it is there nonetheless. For this reason we should accept no gift unless it is given with no motive except pure love. Otherwise we'll be like puppets who jump whenever the invisible strings are pulled.