Verse 5

5. In a secluded place,  sitting in an easy posture,  pure,  with a neck,  head,  and body erect,  living in the last ashram of the orders of religious life,  having controlled all the senses,  saluting his own teacher with reverence,  meditating within the lotus of the heart on The Absolute,  untainted,  pure,  clear and without sorrow.

"In a secluded place,  sitting in an easy posture,  pure,  with a neck,  head,  and body erect"

The ascetic seeking the Absolute Alone is most complete within the Solitariness of his own self. 
Here the ascetic is described in the meditating posture sitting in seclusion.  No other work will be undertaken other than that necessary for the facilitation of meditation.

"living in the last ashram of the orders of religious life having controlled all the senses".

This is the decision of the sage.  "Having controlled all the senses" the sage is now free from the delusion of desire so now naturally renounces the material world as unreal and undesirable to the wise man of higher understanding.

"saluting his own teacher with reverence".

The sage will always be available for his teachers and his realisation of unity will contain insight and understanding of how he or she received that truth.

"meditating within the lotus of the heart on The Absolute".

Here the "lotus of the heart" refers to the higher intellect or Buddhi.  Buddhi is the subtle quality of being that,  in stillness,  has access to "Absolute Knowledge" through which divine reason and discrimination can reveal the truth of the Absolute Itself.
It is from meditation that is free from Manas,  mind and thinking that this higher truth that transcends material Creation is seen or realised through intuition.
With Realisation comes the awareness of this singularity or Non-Duality.  That Singularity is seen as This Alone and all else falls away. 

"untainted,  pure,  clear".

In the course of everyday life one is "tainted" through the perception of duality with its desires and fears.
The sage of this verse,  having Realised the reality of Non-Duality and the Consciousness of the Absolute becomes free "untainted" and "pure" of the impediments of duality.
The sage so liberated has clarity of perception,  his understanding is "clear".

"without sorrow".

"Sorrow" is a product of attachment and the taints of duality,  it is a part of this material Creation. 
The Realised Sage of this verse is "without sorrow" because due to his clarity of understanding he now sees and renounces this material Creation along with its sorrows or joys as unreal and undesirable.

Accordingly the sage renounces the world of the senses without regret or sorrow and through Solitary meditation practice turns to the Absolute within.