Buddha decided to teach what he had learned with the idea, "Some will understand".
Some of his "learning" was likely hunger induced hallucinations. Other were random good insights and summaries. Some are built on the tribal culture and religion of the time and location.
These are only my opinions on the various readings I have done.
Compassion and the elimination of suffering is the main concept. Buddha recognized that suffering is an inside job, a self induced feeling, and that that feeling can be nominalized by a series of concepts, beliefs, values, ways of thinking and actions. Various translations and repeated expressions create a range of ideas of what each component really says. The four Noble truths go something like this:
1. Life contains suffering, pain, impermanence, toxicity, loss, stress, vaguity, distress, depression, pain causing things. The pain is an internal mental object, not a physical reality except if it is our body, but even then, the pain is a mental object. The unsatisfactory quality of life which is targeted mental object, the sorrow and trouble, the never completely fulfilling. We always want more happiness, less pain. But this ‘wanting more’,the longing, is itself the problem, the craving, the desire for more. Buddhism does help the physical, but first, it removes the internal mental object in ourselves.
2. The second part is it is our cravings, our attachments, our selfish grasping after pleasure and avoiding pain that causes the problem. Our delusions of how life should be, our attachment to people, property, prestige, and money, our aversion to loss of people, property, prestige, and money, or simple attachment, delusions, aversions are the cause. Again, these are internal, mental objects. It is not necessarily the real loss, just the potential of loss. Many religions find it easier to have real poverty than deal with the mental potential of loss, or the issues that desire for these things can bring.
3. the third is there is a solution to all this,
4. The solution is following the eight fold path to a peaceful serene state of mind.