Kshara and akshara have been named. Now comes a third reality — one that stands above both. This is the Supreme Being, called Paramatma. He is distinct from the perishable and higher than even the imperishable.
He enters all three worlds — the heavens, the earth, and the realms below — and sustains them from within. Just as a thread passes through every bead in a necklace and holds them together, the Paramatma pervades and upholds everything that exists.
This Lord is avyaya — he does not diminish, does not grow old, does not change. The perishable changes. The imperishable remains steady. But the Paramatma is the very ground on which both stand.