1) “What subject did the Buddha teach?

THE BEST WAY of answering this is to quote the Buddha himself, “Know this, O Monks: Now, as formerly, I teach of only dukkha (suffering, unsatisfactoriness) and the elimination ofdukkha.”

Whether or not this answer agrees with what you had thought, please take good note of it. There are many other ways we may answer, but this one saying of the Buddha sums up his teaching very briefly.

The Buddha taught only dukkha and the quenching of it. This renders irrelevant any questions without a direct bearing on the elimination of dukkha. Don’t consider such questions as “Is there rebirth after death?” or “How does rebirth take place?” These can be considered later.