Karma. What is karma? It's like "vibes," right? That guy's got bad karma. No. A feeling, like, I get bad karma from that girl. Wait, that's vibes.
Karma is action. The Buddha defined it as intention, or intentional action, because it is the intention (motivation) behind an act that conditions its result. A "good" motive will yield a pleasant and welcome result.
What is a "good" motive? The categories are so broad that they are defined in the negative: nongreed, nonhatred, and nondelusion.
"Bad" karma is rooted in greed: craving, lust, selfishness, egotism, callousness, cheapness (nongenerosity), and so on. It is rooted in aversion: hate, fear, anger, annoyance, irritability, and so on. It is rooted in ignorance: delusion, confusion, wrong view, misunderstanding, dogma, ideology, and so on.
Karma, why should we care? We are always generating karma -- seeds with the potential to opportunistically ripen now or anytime in the future when and if they find the right conditions. Given the opportunity, karma bears its results for good or ill, which is usually not the best time.
Moments of weakness may lead to our downfall. Sometimes a reserve of good karma saves us just in the nick of time. So the Buddha says: "To do all that is skillful ("good"), to abandon all that is unprofitable ("bad"), this is the advice of all buddhas." [There have been buddhas in the past, 25 of them in the past aeon.]
We always have a choice, but we often limit the degrees of freedom (as a statistics problem) of our choices until we think we are left with no alternative.
We are always making karma -- be it mental, verbal, or physical -- until we become fully enlightened. Then karma becomes kriya (simple action which does not bear a karmic result in the future). If we approve of others' good or remember good we ourselves have done, at that moment we are generating profitable mental karma.
If we delight in what is unskillful (harmful, greedy, hateful, fearsome, deluded), we are generating unprofitable karma for ourselves. If we speak in praise of the good, we are generating profit for ourselves. If we act for the benefit of ourselves and others and both (society at large), we are storing up merit.
This merit will come in handy because LIFE is long. Life comes after life without end, birth follows birth, consciousness -- even though it perishes just as soon as it arises -- persists beyond death. Karma brings us into being again, brings about our suffering, in and of itself has no escape hatch, no way out. It is rooted out by wisdom.
If by confidence in the Buddha, the Dharma, or noble members of the Sangha one finds the path, then "faith" can be said to have helped, but even then only wisdom (insight) uproots the ultimate source of all misery, ignorance.