The scriptures have directed the usage of Swaha and Swadha while offering the oblations. In a praise of God (Yajna Purusha) it has been said: "Tvamekam Sharanyam" (you are the one and only Refuge for us), "Tvamekam Varenyam" (you are the one and only Choice for us). In the worship of Yajna, Swaha is the mode of dedication and Swadha is the mode of selection or adoption.
There are three interpretations of Swaha-
(1) Su-sushthu ah su - ah; meaning - Good saying.
(2) Sva-vak-ah-iti - A sentence said with ones own voice or with ones assent.
(3) Sva-ahutam - havirjuhoti va - To offer an oblation of havi (materials of yajna) or that of ones talents. The word Swaha is uttered with every offering in the Yajna. The one who conducts Yajna keeps the emotions of the yajaks in accordance with the above rules, but the Yajna can not be said to be complete by this alone. The Yajna will be considered complete only when Swadha is also utilized along with that.
Swadha has also been interpreted in three ways -
(1) To take a definite righteous path,
(2) The act of eating cheerfully
(3) The oblation offered to the manes (departed souls of ancestors) Swadha namah is extensively used in the obsequial rites in the honor of the deceased ancestors. This simply means that the manes should receive the offering cheerfully and get satisfied. The scriptures advise that in the Yajna, YajnaBhagavana must get satisfied, all the invited gods must be satisfied and all the participating-specialists in the Yajna must also be satisfied. Without this, Yajna is not considered complete. This is called the usage of Swadha in Yajna. In this context, Yajna - Bali (sacrifice in Yajna) and Devadkshina are offered. In the context of Bali, it has already been explained earlier that its meaning cannot pertain to killing or any violence. The ritual of offering the eatables/cereals, etc reverentially is called Bali. This has been explained by giving the examples of Devabali, Gaubali, Kakabali, etc and Bali Vaishva Yajna. So in the Yajna, Yajna Purusha and all the invited gods are offered food to their satisfaction; this is called Bali. The Divine powers are also satisfied by expressing thankfulness to them on the completion of work. It is clearly written in the Yajna Mimansha
Balistu trividho jneyastantrikah smarta eva cha / Vaidikashceti.... // Vaidikam tu balim dadyadodanam svinnamashavat / Sarocanamatikrur daivate vatakanvitam //