Saddharmapundarika Sutra or Lotus Sutra in its entirety delivers this:

‘Expose the temporary to reveal the truth;

Conjoin the three, return to being one.’

The temporary denotes expedience, transitory convenience. For, initially

after Sakymuni Buddha attaining enlightenment, termed the original

era of Buddhism during which the Hinayana doctrine had been taught,

practitioners were enabled to realize nirvana with no remaining karma

for suffering and reach the fourth-grade (literally, fruit) arhan position.

In the Lotus Sutra period, broadly did Sakyamuni Buddha come to

teach the Mahayana, in itself a wholly pragmatic format of cultivation

and action. Hence the statement of exposing and disposing of the

temporary to reveal the truth.

In conjoining the three, returning to being one, the first of the three

is the bodhisattva vehicle, the second, pratyekabuddha vehicle, and

the third, sravaka vehicle. Sakyamuni Buddha believes it crucial to

teach the doctrine of the first vehicle, that is, the Mahayana. In the

following is a citation from Lotus Sutra, scroll 1:

‘The Tathagata, via but the one-Buddha vehicle, teaches all living

beings the Dharma. Not via the remaining vehicles such as the second,

such as the third. All past Buddhas—with immeasurable, uncountable

expedience, cause and condition, metaphors and words—delivered to

all living beings varied aspects of the doctrine. Hence such method

pertains to the one-Buddha vehicle.’