उत्तमः पुरुषस्त्वन्यः परमात्मेत्युदाहृतः।यो लोकत्रयमाविश्य बिभर्त्यव्यय ईश्वरः॥
uttamaḥ puruṣas tv anyaḥ paramātmety udāhṛtaḥyo loka-trayam āviśya bibharty avyaya īśvaraḥ
Word by word
The verse says
But the highest being is another: he is called the Supreme Self. He enters the three worlds and holds them up, and he does not wear out - the lord.
In plain words
Neither column, then. A third thing.
He is not the perishing world, and not the unchanging silence behind it. He enters the worlds and carries them.
That word 'enters' is doing a great deal. He is not the world. He is not safely outside it either. He comes in.
Where you've felt this · in family life
Shanta raises three children, runs a house and keeps a job at a school for twenty-two years. Ask the children what she is and you get three answers, all true and all too small. She is not just the cooking, and she is not some separate person hiding behind the cooking. She is in all of it, and none of it uses her up.
Going deeper
Something can be completely involved in a thing and not be used up by it, and that is the claim being made.
Puruṣottama means the highest person. Not the changing world, and not the changeless quiet either. The verb is 'enters'. He goes into the three worlds and holds them up from inside them.
This is the Gita's answer to a problem every religion runs into. A God who simply is the world cannot be turned to, because there is nobody there to turn to. A God entirely outside the world cannot be reached, because the distance is infinite. A God who enters and sustains is near enough to matter and large enough to help.
It also quietly settles something about you. If the highest thing is personal, if it has come in, then your relationship with it does not have to be dissolved in order to be real. You get to stay someone.