In the Root Tantra of Chakrasamvara, it says the supreme attainment can be accomished merely through reciting the mantras such as the 3-OM mantra of Vajrayogini, however, there are various meanings of this.
It doesn't mean that the mantra recitation is the only condition by which the final Union of No More Learning is attained, but through the recitation all the conditions for accomplishing the common and supreme attainments can be produced. How quickly it produces these conditions depends on the altitude of the practitioner, the degree of their faith, correct view, correct intention, level of concentration, frequency of application and so forth. This is a wonderful encouragement actually. Even if a practitioner recites with a little faith and poor concentration, powerful imprints will be left in their mind, and it will also start to gather conditions for faith, concentration, and other good qualities and conditions to increase.
Strictly speaking, it is necessary to gather many conditions together to complete the path. In particular, it is finally necessary for the practitioner to progress through the actual completion stage meditations. Vajra Recitation is the ultimate mantra recitation and we can understand how this leads to the attainment of final enlightenment by studying commentaries on the practice.