Andrew Skilton addresses this in the 10th chapter of A Concise History of Buddhism: "It seems that the Abhidharma proper grew out of, or was built around, mātṛkā--i.e. lists of technical concepts, originally serving as mnemonic devices for memorizing teachings...For example, the ubiquitous list of 37 bodhipakṣika-dharmas, or 'teachings that are requisite for Awakening' may have been an early example, given by the Buddha himself. We have another early example of this tendency in the Saṅgīti Sutta where Sārīputta, who is traditionally associated with the origin of the Abhidharma, recites lists of teachings arranged according to number."
namo bhagavate śākyamunaye tathāgatāyārhate samyaksaṁbuddhāya | namaḥ sarvabuddhabodhisattvebhyaḥ ||
"Bodhisattva-mahāsattvas love all beings in the world equally, as if each were their only child..." Buddhāvataṃsakamahāvaipulya Sūtra