The big break between the Mahayana and the Theravada is the idea of the bodhisattva — a being whose practice is not aimed at personal liberation, but the liberation of all beings. The Bodhisattva path is the path to Buddhahood after one becomes a Bodhisattva. The steps to becoming a Bodhisattva and the further steps towards Buddhahood are referred to or outlined in many sutras, most notably the Avatamsaka Sutra.

For more information see https://en.wikipedia.org/wiki/Bodhisattva