Visákha visits Dhammadinná and asks her a series of questions on personality, the Noble Eightfold Path, plastic forces (sankhárá), etc. Dhammadinná explains these things to Visákha, who then consults the Buddha as to whether the explanations are correct.
The Buddha tells him that he himself would have given the same answers and praises Dhammadinná's erudition (M.i.299f).
The sutta forms a kind of commentary on certain psychological terms, such as sakkáya, sankhára, etc.
See Vedalla.