Sutra:
33. mUnRu thAzhiyilE thayirai niRaiththuk kadainthu veNNai thirattinARpOlE mUnRu vEthaththilum mUnRu aksharaththaiyum eduththathu.

34. AgaiyAl ithu sakala vEtha sAram.

Meaning:
33. This is like collecting buttermilk in three vessels and extracting the butter from them. The essence of three Vedas has been extracted in the form of the three aksharas.

34. Therefore, the praNavam is the essence of all Vedas.

Sri PBA Swami's Sarartha Deepikai (33 & 34):
Previously it was said that samhitAkAram can be used to explain the sruti "OmityEkAksharam", while asamhitAkAram can be used to break the praNavam into three aksharas. Is the use of asamhitAkAram acceptable, as it goes against the sruti?

Here it is shown that the srutis accept the breaking up of the praNavam into three aksharas and that the three aksharas are the essence of three Vedas.

The aksharas that make up the praNavam are "a", "u" and "m". These arise out of the Rk, Yajur and Sama Vedas. From these three Vedas come the Bhu:, Bhuva: and Suva: (the three great vyAhRtis) which were created and run by Him, and He stood within them and created these three aksharas. Therefore, this is bringing out the essence of the Vedas, which is like bringing out the butter which is the essence of buttermilk. Are there srutis to support this? There are, such as "pUriti rkvEdAt" and others.