Sutra:
35. ithil akAram Sakala sabthaththukkum kAraNamAy nArAyaNa pathaththukku SankrahamAy irukkaiyAlE, Sakala jagaththukkum kAraNamAy SarvarakshaganAna emperumAnais sollugiRathu.

Meaning:
The first akshara amongst the three aksharas of prAnavam, is akAram ("a"). This akshara is the cause for all the sounds (words); it also stands for NarAyaNa padam which itself stands for one who protects all. Thus akAram stands for Him who is the cause of all and the protector of all.

Sri PBA Swami's Sarartha Deepikai:
Here the meaning of the first aksharam is explained. The meaning of akAram is He who is sakala jagat kAraNabhUta (cause of all worlds) and sarva rakshaka (protector of all).

How are these brought out by akAram?
There are two rules to consider: prakruti sakthi and dAtu sakthi. The prakruti sakthi brings out the causal nature and the dAtu sakthi brings out the protective nature.

Prakruti means natural being. The natural disposition of akAram is that it is the source of all sounds (as in the Thirukkural "akara muthala ezhuththellAm"). Sriman Narayana has a similar nature, of being the cause of everything. By this similarity, akAram stands for Him who is the cause of all.

akAram also represents the dAtu "ava". This dAtu stands for protection as in "ava rakshaNE". Thus akAram also stands for Him who is the protector of all.