Whether standing or walking, seated or lying down
Free from drowsiness,
One should sustain this recollection.
This is said to be the sublime abiding.
By not holding to fixed views,
The pure-hearted one, having clarity of vision,
Being freed from all sense desires,
Is not born again into this world.
To me, to be free from drowsiness means to be mindful. We are mindful of the moment in all situations, and 'sustain the recollection' of lovingkindness to all beings. This loving state of being is the 'sublime abiding', which some paraphrase as the 'divine abode', or dwelling-place of gods, but to me it's more literal. 'Sublime' means supreme, most high or of most spiritual worth, and 'abiding' means 'enduring' or 'lasting for a long time'. So lovingkindness is the state of being of highest worth that ought to endure.
The Buddha teaches that we should not hold to fixed views. We should remain open-minded about everything, and test everything to see if it is true. Thich Nhat Hanh's first and second mindfulness trainings reflect this well:
Aware of the suffering caused by fanaticism and intolerance, we are determined not to be idolatrous about or bound by any doctrine, theory, or ideology, even Buddhist ones. Buddhist teachings are guiding means to help us look deeply and to develop our understanding and compassion. They are not doctrines to fight, kill or die for.
Nonattachment to Views
Aware of the suffering caused by attachment to views and wrong perceptions, we are determined to avoid being narrow-minded and bound to present views. We shall learn and practice nonattachment from views in order to be open to others' insights and experiences. We are aware that knowledge we presently possess is not changeless, absolute truth. Truth is found in life, and we will observe life within and around us in every moment, ready to learn throughout our lives.
Sense desires are one of the Five Hindrances. (They include sense desires, anger/ill-will, sloth, worry and doubt.) They are the craving of senses, the craving to get what you want. (There are six senses in Buddhist thought: eyes, ears, nose, tongue, body and mind; ie, sight, sound, smell, taste, touch and perception/mental formation.) So we're not just talking about wanting a bowl of ice cream or a warm bed, but also wanting attention, accolades, wanting knowledge, all sorts of cravings and wants driven by clinging.
'Clarity of vision' is the ability to see that there is no end to suffering to be found in striving to fulfil sense desires. In fact, is the attempt to find fulfilment through sense desires that leads to suffering, or as Thich Nhat Hanh translates it, 'ill-being.' (The original word is 'dukkha'.)
The last line of the metta sutta holds some problems for me. The traditional sense of reaching nirvana means to not be born again into the world, ie, not reborn or reincarnated. This is something I haven't wrestled much with in my mind. I have some thoughts on it, though. More on that later.
May all beings be at ease.