This sound [OM] is remembered with deep feeling for the meaning of what it represents.
Repetition of That [OM] means to contemplate the meaning of That.
To repeat it [OM] with reflection upon its meaning is an aid.
Following on from the previous sutra, when we repeat the sound OM, we are practising japa (repetition). Sri Swami Satchidananda says that when you have the habit of repetition, you can think about the meaning (god, according to the sutra).
I must admit I am struggling somewhat with the evocation of ‘god’ in this section of the sutras – I am an atheist Zen Buddhist, and the concept of ‘believing in’ a supernatural deity is difficult. I am trying to widen the meaning to mean ‘universal energy’ or ‘personal inspiration, rather than ‘god’ as such. But is it possible to live a ‘yogic’ life according to the eight limbs without a belief in a ‘god’ of some kind? To try to reconcile this, for my own practice, when I repeat ‘OM’ at the beginning and end of my asana practice, I will try to think about it connecting me with the energy of the universe.