The word ‘Sat’ is employed in the sense of the ultimate Truth, Reality, as well as goodness and nobility. O Partha, ‘Sat’ is also used to refer to any act esteemed for loftiness or auspiciousness (because such work helps one attain the Truth).
The third word of the triplet is ‘Sat’. It denotes something good, noble and great. But the main meaning it carries is Truth, Reality, the singular all-pervading changeless Presence. In one sense it indicates Brahman, the Self, the indwelling sentient presence, the ‘I’, which is not subject to any change at all.
Sat is used as a prefix to many words, indicating what it refers to is auspicious, lofty or benevolent. The reason is that any such auspicious act or word relates one to the path of ultimate Truth.
Sat-karma, Sat-śraddhā, Sat-purusha, etc. are words in which ‘Sat’ is prefixed. Like Om and Tat, Sat represents goodness and its derivations. All the three words have the power to instil purity and divinity anywhere, especially while one embarks upon any important undertaking. They are a subtle spiritual force, which can influence an entity, a place or purpose!