A geas was a contract with the goddess of Fate. Sometimes one was born indentured, other times it was bestowed upon one as a curse. Because if one did not fulfill the terms of one's geas, one died. It was old magic, the magic of the gods, spoken in the tongues of those who controlled the dragons - and it was supposed to be extinct.
Your heart's voice is your true voice. It is easy to ignore it, for sometimes it says what we'd rather it did not - and it is so hard to risk the things we have. But what life are we living, if we don't live by our hearts? Not a true one. And the person living it is not the true you.