(From the) origin (Brahma) come the three realms of material, experiential, and emotional, (may they be bathed in the) ray of Savitur, and bring us closer to that deity of glorious light.
Note:
(1) In the Brahmanical i.e. Non Puranic, Vedic tradition, Brahma is not part of a trinity. From Brahma comes his light Mitra who together with his fluid Varuna and matter Aryama form the cosmos. Mitra forms and sustains 12,000 types of Suns. From the Sun comes his light Savitur (father) comprising the three Gunas of Virinchi (creative etc), Narayana (sustaining etc) and Shankara (transcreative etc), who, as light, warmth etc (Sandhya), life etc (Savitri), sound etc (Gayatri) and knowledge etc (Sarasvathi) forms and sustains life here in unison with water (Aapa) and soil (Bhu) the two mothers:
(2) Gayathri is the meter to which the invocation of Savita is set by Brahma Rishi Vishwamitra. It is not a Manthra. Many Rishis have set many different invocation to the Gayathri Meter: