Phurpa Tashi Rinpoche
From the perspective of cause-and-effect never failing, every virtuous action (including reciting mantras) produces merit. But no teaching says that one can be reborn in Sukhavati without training the mind. Where does accomplishment or attainment come from? It comes from practice with the mind as the central point, otherwise known as mind training.
Buddha Shakyamuni taught 84,000 Dharma teachings, encompassed within the Three Vehicles, with the central aim being: “Purify one’s own mind.”
Patrul Rinpoche once said that the Mani mantra is the essence of all the mantras of all the Buddhas and Bodhisattvas in the three times and ten directions, but if it is recited in a distracted state with a scattered mind, it carries no merit at all because the practitioner is not countering his/her own afflictions.
This shows that if we base our understanding of merit solely on the quantity or outward form of our virtuous actions, it is difficult to attain liberation.
Therefore, no matter what virtuous practice one engages in, one must observe and train the mind with the view to increase renunciation, Bodhichitta and faith, as well as to decrease the mental afflictions.
(Note: Distraction itself is a secondary mental affliction according to the Abhidharmasamuccaya)