This painting is about states of mind while meditating.
Meditation involves the closing down of the senses and withdrawing from the outside world, you close your eyes, focus on your breathing and still the mind to achieve a state of relaxation and peace. I've used underwater scenes to convey the feeling of meditating, as when diving, your senses are also closed down to some extent; hearing is considerably reduced (your own breathing seems to be the loudest sound) and field of view and distance you can see is also reduced. The pressure on your body is alien and enforces the 'other worldliness' of diving.
So in meditation we try to leave worldliness behind, to have a still mind, to think no thoughts, and ultimately, one day, to reach enlightenment (!). Barriers to meditation, or simply being calm, are ones own ego and persistent thoughts and worries that insist on invading our heads.