I am not sure where I heard this comparison — maybe in the Dalai Lama’s The Art of Happiness book. He and Trappist Catholic monk Thomas Merton were friends. Merton’s description of the spiritual process, in books such as The Seven Storey Mountain, is one of going within oneself, away from the outside world, as if climbing a mountain. At the top, one is left with only oneself and very little of the world. One can only call to God and wait/hope to be raptured (rapture has the same word root as raptor and rape, meaning to overtake by force; the image is of God swooping down and carrying one away from the world into the heavens). At some point, there is nothing more a person can do on the spiritual journey, and it becomes all up to God.
By comparison, a similar Buddhist metaphor is that there are two shores (perhaps of a river or of two islands), which represent two different states of being: one shore is samsara and the other nirvana. It is not evident how the two shores came into being, but the two always exist side-by-side, and the shores are visible to/from each other, if one looks hard enough. Most people spend their lives just walking up and down this samsaric shore. Very few people abandon this shore, jump in the water, and make the effort to swim to the nirvanic shore, but the process is possible through personal effort alone. There also are “vehicles” (i.e., traditions of Buddhism; Mahā-yāna means great-vehicle) that can ease the crossing.