Scope of Buddhism & Outlook of the World
It is necessary to have many "vehicles" in Buddhism because there is no one single school of teaching to lead all people to the Buddhist Way.
Literally, the Great Vehicle means a greater vehicle to liberate more people from suffering.
A Praetyka-Buddha is an Arhat who is still subjected to the bondage of the cycles of birth and death.
All Bodhisattvas have common vows of seeking Buddhahood and transforming sentient beings.
From the Buddhist point of view, the theories in Human & Deva Vehicle and Two Vehicles are contradictory to each other because the former emphasizes our existence of blessings, etc., while the latter emphasizes on non-existence and emptiness.
One Buddha Vehicle is the ultimate truth and all other vehicles in Buddhism are not.
Ten Dharma Realms are not beyond a single thought.
Human Path is better than Deva Path in the sense that man has a better chance to pursue Buddhist Way.
There are only ten titles to describe Buddha.
Six Paramitas and Four Immeasurable Minds are used by Bodhisattvas in rescuing sentient beings from suffering.