Aarti is said to have descended from the Vedic concept of fire rituals, or homa. The word may also refer to the traditional Hindu devotional song that is sung during the ritual. Aarti is performed and sung to develop the highest love for God. "Aa" means "towards or to", and "rati" means "right or virtue" in Sanskrit.
The Gayatri Mantra occupies a unique place in that it has both the power of mantra and of prarthana (prayer). It is important then in considering the Gayatri Mantra to distinguish the difference between these two deceptively similar words.
A mantra may be articulate or inarticulate, or a combination of them, as with AUM. It has an inherent power, known as "Mantra shakti", which has a positive influence not due to any philosophical meaning behind the mantra, but simply due to its utterance alone (of course, "utterance" may or may not be vocal or heard - it can be silent, expressed only in the mind, or at the deepest level, heard only by the soul itself). As explained, a pure mantra may or may not have any actual meaning or philosophical significance, its power being intrinsic to the mantra itself, and not instrumental to any meaning.
A prarthana on the other hand does have a philosophical meaning behind it, and it is generally through this meaning that the prarthana has its power. Since the mantra is devoid of any kind of actual meaning, it cannot be conceptualised or visualised. This makes its understanding extremely difficult to the normal human mind, thus rendering its correct enunciation almost impossible to the untrained person. A prarthana however, having a meaning that can be comprehended through purely intellectual means, is far easier to be understood, since rational thought, unlike spiritual meditation, is much more in the reach of the ordinary person. Thus, the method of prarthana is generally the form of worship used today.
The Gayatri, or Guru, Mantra possesses both the power of mantra and the power of prarthana, and thus has both an intrinsic power (ie "mantra shakti"), through its mere utterance alone, and also an instrumental power (ie "prarthana shakti"), which is derived from the exposition and understanding of its meaning and philosophical significance. The repeated and correct chanting of the Gayatri Mantra, with proper understanding of its meaning, is believed to be of the greatest good to the individual.
AUM BHOOR BHUWAH SWAHA,
TAT SAVITUR VARENYAM
BHARGO DEVASAYA DHEEMAHI
DHIYO YO NAHA PRACHODAYAT.
Oh God! Thou art the Giver of Life,
Remover of pain and sorrow,
The Bestower of happiness,
Oh! Creator of the Universe,
May we receive thy supreme sin-destroying light,
May Thou guide our intellect in the right direction.