Vyasa collected a subset of Mantras which were in vogue at the end of the last Yuga or Era. He created four compilations. Several mantras are common between the Rig, Yajur and Sama Veda compilations. Almost all Sama Veda mantras is in the Rig Veda compilation. Not all mantras of Rig Veda are in the Yajur Veda compilation. Yajur Veda contains manrtas which are not in the Rig Veda compilation. The reason behind this as follows

The first act in the Yagya is to invite appropriate Devas to the Yagya which is being conducted. Rig mantras are chanted to invoke the energies of Devas in the Yagya fire alter. Offerings to Devas is the second major aspect of a Yagya. Yajur Veda priests sanctify the offerings using mantras and place them into the Yagya fire also while chanting the mantras of appropriate Devas. Sama Veda priests seek blessings from the Devas towards the end of these offering by chanting Sama Veda mantras. Saman chants touch the heart of Devas. They in turn grant the fruits of the Yagya to the performer.

A mantra unsually addressed one Devas and sometimes a group of Devas. All three classes of priests may use a common mantra to address the same Deva. The intotations distinguish the purpose for which the Mantra is being chanted. Musical notes characterise Sama Veda chants. Sama Veda is the precursor to classical Indian music. There is a distinct style of chanting for the Rig Veda and the Yajur Veda. A casual listener can also begin to distinguish this when the same Mantra is chanted one following the other in the Rig and the Yajur chanting styles. The following is a beautiful rendering of a few popular mantras in the Rig and Yajur style of chanting.