THUSNESS
Now, we come to the fourth and last topic: tathata (suchness, thusness). "Merely thus," "just such": everything is such as it is and in no way different from that thusness. This is called "tathata." When tathata is seen, the three characteristics of anicca, dukkha, and anatta are seen, sunnata is seen, and idappaccayata is seen. Tathata is the summary of them all -- merely thus, only thus, not-otherness. There is nothing better than this, more than this, other than this, thusness. To intuitively realize tathata is to see the truth of all things, to see the reality of the things which have deceived us. The things which delude us are all the things which cause discrimination and duality to arise in us: good-evil, happiness-sadness, win-lose, love-hate, etc. There are many pairs of opposites in this world. By not seeing tathata, we allow these things to trick us into believing in duality: this-that, liking-disliking, hot-cold, male-female, defiled, enlightened. This delusion causes all our problems. Trapped in these oppositions, we can't see the truth of things. We fall into liking and disliking, which in turn leads to the defilements, because we don't see tathata.
What we must see constantly and deeply is that good is a sankhara and that evil is a sankhara too. The pleasant and unpleasant feelings, sukha and dukkha, are both sankhara. Getting and disappearing, losing and winning all are sankhara. There isn't anything which isn't a sankhara. Thus, all things are the same -- tathata. All things are just suchness, just this way, not otherwise. Further, we can say that heaven is a sankhara and hell is a sankhara. So, heaven and hell are tathata -- just thus. Our minds should be above heaven and above hell, above good and above bad, above joy and above dukkha in all respects. Tathata is the fourth area of understanding or paññä, the wisdom that must be developed to a sufficient degree. We must study reality on both the physical-material level and on the mental-spiritual level, until our knowledge and wisdom is adequate, natural, and constant.
http://www.dhammatalks.net/Books/Bhi...l_Disease2.htm