There are different levels on which a mantra functions or may be employed. Awareness of them, along with honest assessments of one's internal mental growth and present state, can prove to be helpful. I am also contrasting them with the theology of the four common aspects we know as nama, rupa, guna and lila.
* Concentration. Objective: Training the mind. Mechanical chanting operates on the mind in a technical capacity. The idea of just blocking away all thoughts while focusing on the sound of the mantra was once much scorned upon; yet this approach does serve as excellent concentration practice. The mind needs to be trained for further levels of employment, where an unflickering, one-pointed nature is imperative and vital. Focus on a supramundane object, even if the mantra is taken in a capacity falling short of its fullness, also contributes to the purification of the engaged faculties. Focus on the sound, as skillful concentration practice in general, also lets the mind rest in solace at times of strain. This level corresponds to "Nama".
* Prayer. Objective: Healing the heart. Chanting in a contemplative, prayerful mood is vital for developing an ability to introspect, for cultivating virtue in one's nature. It is only through honest prayer that one comes to terms with one's innermost core, pulls out the muck and resigns in humility. As much as prayerful mantra is a call for the deity of the mantra, it is a method for spiritual self-healing. In this, the external formulae of the mantra tend to at times subside as the mind plunges into the heart and arises with emotional responses to the contemplative discoveries of one's being. This level corresponds to "Guna".
* Static visualization. Objective: Internalization. Coined mantramayi-upasana, the practice of visualizing a static object or scenario serves both as concentration-practice as well as in internalization of the meditation-object; one gradually imports the contemplated scenario, often an other-worldly reality, into a part of one's current internal reality. The various mula-mantras and gayatris are particularly suitable for this practice. In contrast to the first two approaches to chanting, chanting employing the visualization faculty is substantially more difficult. On this level, the mantra may be experienced as one with the object of vision. This level corresponds to "Rupa".
* Dynamic visualization. Objective: Residing in the flow. Coined svarasiki-upasana, this level combines the essence of prayer in the way of a developed emotional attitude and identity with the internalized other-worldly static vision-reality into a dynamic, flowing interplay. While the other three levels are easier to practice, dynamic visualization requires substantial accomplishment from the participant; in absence of that, not much beyond hazy and flickering projections are to be unveiled. True to its name, this level is one of a natural flow, no longer depending on the force of effort for its sustenance. On this level, the mantra may be seen to dissolve or rather form into the flowing fabric of the vision. This level corresponds to "Lila".
One should not think that the above levels are mutually exclusive; they may be employed at appropriate times to address the current need. In fact, it would be less than wholesome a practice to omit some of the above on a stage prior to seamless residing in the meditative flow, where the core of the other three levels combines, and as such no substantial omission happens despite the technical absence of isolated level practices.
It may be of interest to readers to note that the fourfold correspondence to nama-rupa-guna-lila was the last factor I added to the above; after outlining the four levels, I realized the obvious parallel of the four basic levels I am, at least conceptually, familiar with through contemplation. A bridge from doctrines to experiences should be built for a thorough understanding of the realities at play.
Formulating concepts without reliance on a technical theological framework can make a substantial contribution for understanding. The framework serves better as a means of refining the experience-rooted understanding than it does as the primary foundation and fabric; for the latter can often be hollow and insubstantial in all of its sophistry, owing to a lack of internal connection.