Verse 19

19. In me alone is everything born,  in me does everything rest,  and in me is everything dissolved.  I am that One Alone without a second.

"In me alone is everything born,  in me does everything rest,  and in me is everything dissolved"

"me alone" refers to Absolute Consciousness.  The meaning is that all experiences of individuals,  groups,  birth,  death and so forth take place "in" the One Consciousness.

"I am that One Alone without a second"

This is confirmation of the above meaning which is to say Existence is not made up of many forms all joined by one thing to form a contrived unity.  The Truth is literally that Consciousness Alone Exists and all apparent diversity is merely an experience within that Singularity of Consciousness.

You Alone are all.  Kaivalya,  the Solitary realisation of Alone is the great responsibility this Upanishad is trying to wake us up to.  You cannot share this responsibility with others because "others" are not the reality of Existence.  All perceptions,  thoughts,  ideas and concepts can be allowed to fall away,  Nothing needs to be retained.  when all is gone your infinite Self alone remains.  This is not easy to achieve,  courage and great faith in the truth is needed.