Impeccability means "without sin." Religions talk about sin and sinners, but let's understand what it really means to sin. A sin is anything you do which goes against yourself. You go against yourself when you judge or blame or reject yourself.
Self-rejection is one of the biggest sins you can commit. Being impeccable is exactly the opposite. You take responsibility for your actions, but you do not judge, blame, or reject yourself.
Being impeccable with your word means using your energy in the direction of truth and love for yourself. If I see you in the street and I call you stupid, it appears that I'm using the word against you. But really I'm using the word against myself, because you're going to hate me, and your hating me is not good for me. Therefore, if I get angry and with my word send that emotional poison to you, I'm using the word against myself.
If I love myself, I will express that love in my interactions with you, and then I am being impeccable with the word, because that action will produce a like reaction. If I love you, then you will love me. If I insult you, you will insult me. If I'm selfish with you, you will be selfish with me. If I use the word to put a spell on you, you are going to put a spell on me.
You can measure the impeccability of your word by your level of self-love. How much you love yourself and how you feel about yourself is directly proportionate to the quality and integrity of your word. When you speak with integrity, and say exactly what you mean, you are impeccable with your word; you feel good; you feel happy and at peace.
~Don Miguel Ruiz