The "collections of merit and sublime wisdom" refer to method and wisdom, the two fundamental factors that lead toward enlightenment and liberation. They are interpreted according to the level of teaching. In general, they refer to bodhichitta (method) and perception of the emptiness (wisdom). Ultimately, these two are inseparable, but for the sake of understanding, they are divided.
In Tantrayana, they are symbolized in this way:
...which also reveals the way in which the two collections are most rapidly realized.
The two collections are synthesized as Upright View, which is the ground from which all true virtue springs. That is why it is the first of the eight steps of the path.