Inge wrote:So many people speak about samaya, but it is my impression that they, like me, have no idea what samaya really is.
I have never read a satisfactory explanation, neither in books, nor online. Nor have I heard any teacher explain this properly.
In your knowledge, what exactly is samaya?
Samaya is making a promise and keeping it. Its that simple. Some are made to yourself, some are made to all beings (bodhicitta), some are made to the Guru, Dakini, Buddha... whoever.
What is special about Samaya is that it is coupled with Bodhicitta. The promise is a sacred one and an extremely important one, it is intrinsically tied into your intention to achieve Enlightenment for the benefit of all beings. In my opinion Bodhicitta is the ultimate and the only samaya.
It works because making and keeping promises generates good merit. Merit is basically a storehouse of good deeds. Its separate from karma because karma is based on mental patterns, habitual ways of projecting images onto empty appearances and this in turn determines where we will appear/be reborn, what circumstances we will find ourselves in, and how we will react to our environment. Merit on the other hand is accrued by performing conventionally good karmic actions, and specifically merit grows whenever you follow through on your intention to achieve enlightenment for the benefit of all beings. If that means a special samaya to your tantric guru or the Dzogchen samayas or a set of vows. The important thing is to first of all do your best to keep the promise without breaking it, and secondly if you break it to repair it as soon as possible, with heartfelt intent to not repeat the breach of samaya. Follow through generates merit.
For example, the six perfections. With Bodhicitta, you make the promise to be generous. Therefore, you give money to someone. You do this with the intention to reach enlightenment for the benefit of all beings, and when you perform this action (based on how selfless it is) you accrue good merit. You've followed through on your intention. You've strengthened that mental karmic pattern as well, so you will only be more likely to do it again in the future. This is how merit grows until it is an overflowing ocean. Each follow through just makes the next one easier.
If you fail to follow through again and again, you are breaking your promise. When you break your promise, you lose merit. You cant keep your word. You weaken your will and people will take what you say less seriously because literally you no longer merit being listened to. However, if you have remorse and really try to repair the broken promise, most people will forgive you, and that is all that the Bodhisattva path asks of the practitioner. Do your best, always repair your broken promises with good intentions and strong resolve to not repeat the action again.