To be certain of reaching our destination when undertaking a long trip, in addition to getting rid of anything that can create obstacles, we need to bring along provisions and other essentials for the trip.
On the Buddhist path, that corresponds to the stage called “accumulation” (merit and wisdom).
In other words, to make purification possible, it is necessary to fulfill a number of requirements and conditions. That process is called “the acquisition of merit and wisdom.”
The acquisition of merit is achieved by the practice of the first five transcendental virtues: generosity, discipline, patience, joyous effort, and concentration.
The acquisition of wisdom, the sixth transcendent virtue, comes from recognizing the ultimate nature of reality.
Source: Taken from Ricard, Matthieu. On the Path to Enlightenment: Heart Advice from the Great Tibetan Masters. Shambhala. Kindle Edition.