That Was Emptiness!
There is little agreement between buddhist schools and lineages about what is what and the qualifications. Some have low standards, some high, some think they have high standards when in fact they have low standards. The point is that there is little consensus, so who can be considered an authority?
Anyway, buddhism is concerned with confusion and removing of it. That's all buddhism is meant to do and the way it is done, is through the emptiness principle. Emptiness or selflessness means that we come to perceive ourselves and all things in our mind, having no solidity, no entityness, no fixed existence. That's all. Everything else is just an elaboration of this core teaching. This very point removes all of our problems, because it removes all of our narrowminded selfing.
Stream entry is known by most schools of buddhism, although the names vary and the methods of getting there vary. For the sake of clarity and simplicity I'll call it awakening. What is awakening? What's the point of it?
We have basically two minds: 1. basic mind that is clear, pure, untainted and without confusion and 2. confused mind that is the construction of the self, in various forms. We are confused because we are stuck in the self-based mind, without knowing the basic mind and that the confused mind is actually also the basic mind. The purpose of vipashyana meditation, that is typical to buddhism, is to enable us to see that me, my thoughts, my emotions and my subtle body is actually the basic mind that is free and has no confilct. The purpose of buddhist meditation is to see and realise this simple fact. This realisation comes about through glimpses, awakening and integration. Awakening or stream entry is the first irreversible hit, or a blow, that causes the sharpest peak of our selfing to collapse, so that it won't reconstruct. This cannot be accomplished through calmning down meditation, although it is useful in the process.
An analogy of a glimpse, where a dog represents the basic mind that has no self. Imagine you are sitting in front of a small window, hoping to see the dog on the other side of it. If we haven't seen the dog, we don't know what to expect, even if we know other people's descriptions of it. Then, out of nowhere, the dog runs past the window. Swoosh! All we see is smudge run by. We are not completely sure how the dog looked because it went by so quickly but we saw it well enough to see that it had four legs, a tail, two ears and had the general appearance of a dog, just like the dog specialist said it would. This is a glimpse of the basic mind. It is something but it is not enough for us to see the dog well, so that we'd have certainty about the dog.
Awakening is different from glimpse. You sit behind the window again, hoping to see the dog, and then all of a sudden it comes, sits down, right behind the glass for a brief moment, during which you can see it perfectly for the first time ever, until it stands up and runs away again. Ah! That's it! That was the dog! Woohoo! Maybe you have such initial joy and wonder, many do. After the initial excitement passes, you realise that seeing the dog has somehow changed you. You no longer feel the same as before. Something is clearly different and its so much better now. You feel more you, freer, clearer, more natural, chest doesn't feel heavy and so on. It's all because you saw the dog, your true nature, without "you", the entity, in it. And because you did, it deconstructed your sense of self as an entity. That's why you feel different post-awakening. Now you gained unshakable certainty about the dog.
Whether we call this awakening, kensho, stream entry or anything else, is of no importance. The importance is on what it does to one's confusion and dissatisfaction, that, as I said above is the heart and soul of buddhism. What matters the most is how our confusion, or self, comes torn down, or seen through.
Now, some say that awakening is this or awakening is that, and are keen to deny if some single specific criterion is not checked. "You're still getting angry, huh? Well, that wasn't stream entry then". "You can't have your finger chopped off, without screaming on top of your lungs and becoming grudgeful against your abusers? Oh, you certainly didn't wake up!". As I said, there is little consensus but the way I see it, is like I explained above. What matters most is the selfless hole in the mind, that no longer has selfing in it, and that is also what is most meaningful for the person her- or himself. Whether one can read other peoples minds, walk on water, have light shining from one's heart, see past lives and so on, are just side dishes, somethign extra that you can do without. Emptiness is the main meal that fills the belly.