According the sutta’s Buddha was confronted with sickness, decay and death. He was deeply affected by that, realising he was himself of the same nature. I feel this is so humane. One can be really for long more or less be insensitive for the reality of sickness, decay, death. But when it becomes personal, things change drastically. Many people become really disturbed, anxious, even in panic mode. This is so normal, so humane. We can only sympathize with this i feel.
Buddha also developed a sense of urgency according the sutta’s: ‘What is the escape from all this suffering’?
Reflecting upon the cause of suffering
He reflected upon the question: What causes this sickness, death and decay? He came to realise: it is birth (SN12.10, DN14).
Quite a sobering insight . Who does come to such an insight? But true. Without birth in some existence this suffering does not occur. Here in the Netherlands, not raised with the idea of rebirth, probably no person reflects upon the cause of decay, sickness and death in terms of birth. And no person aims at ending birth, or seeking the causes of birth. If we seek the cause of sickness we seek that in a medical way. The same with death and decay. I feel this says that rebirth must have been part of Buddha’s understanding from the start of his search (or we must see this description of Buddha’s search as legendary, mythical, which i choose to do not).
I believe his awakening can be seen as perfected knowledge or insight into how birth takes place and ends. He was seeking what causes birth and his insight into this was perfected when he attained full enlightment.
In 3 ways a perfect insight into birth
He saw his own births, his former lifes. This was his first knowledge about birth. He saw that he had many times taken birth before and saw that he was then this, then that. Rebirth was for him now not a cultural load anymore but his direct knowledge.
Moreover, he saw how beings according the views they grasp and the volitional deed sbased upon them (kamma) are reborn in a certain realm of existence. He saw this law of kamma. How view, volitonal and result relates. He saw that view is very important because based upon how we understand things, we have certain plans, intentions and tendencies. Wholesome or unwholesome. Those shape our future, even our next existence. He was even able to see the rebirth places of beings that died with the perfected heavenly eye.
Moreover he saw how birth relates to defilement (asava, tanha), but not to purity. He saw and realised the end of all asava (Nibbana, perfect peace and coolness, purity). He understood the Path to end birth, i.e realising this purity.
For me this means that he understood that purity does not take part in birth, decay and death. By this he was confirmed that with the realisation of Nibbana, purity, he realised the end of rebirth. His task was done. He wanted to understand birth as cause for decay, sickness, death and he came to understand birth as caused by defilements that arise based upon wrong understanding (avijja). So, i believe, that the mind or knowledge that is pure, that is totally free of any defilements, grasping, attachment, that also knows that it is free of birth, decay and death.
I believe that Buddha got confirmation about the end of birth from realising that dimension that was, is and will always be free from birth, decay and death. The sutta’s point to this dimension in short as asankhata, that dimension free from grasping, uninclined, desireless, empty. That what has no characteristics to arise, cease and change.
He saw and realised what was, is and will always be beyond any bhava, Nibbana, that dimension that is not constructed. Unworldly peace. Because it is not constructed it is not a bhava. The housebuilder was seen and destroyed (dhp) in this very life.
I believe, not knowing this pure dimension, Nibbana, the unconstructed, unworldly peace, we and other beings always seek protection, safety, an escape from suffering in external things. Because we see no other Path. The ignoble search. But because this peace is there, there is an escape. There is a Path. There is a refuge. There is protection.
Maybe this more esoteric understanding of Dhamma is not appreciated here, but personally i see no other way how we can be confirmed that birth is ended by seeing that unwordly peace, Nibbana, purity, does not take part of birth, does not decay, get old, become sick, and does not die.
To ignore this peace we have always done. We have always only be obsessed by formations coming and going. I feel, Dhamma invites us to make a change.
This makes sense to me, at least.