About this passageThe Mettā Sutta, among the most widely recited texts in the Theravāda world and often chanted daily. It begins with ordinary conduct — be easy to speak to, be unburdensome — before it reaches the famous image of the mother, and the instruction it gives is to extend the same regard outward without selecting a recipient. The list of beings is deliberately exhaustive.
Let them be capable and upright, very upright, easy to speak to, gentle and humble; content and unburdensome, unbusied, living lightly, alert, with senses calmed, courteous, not fawning on families.
May they be happy and safe! May all beings be happy! Whatever living creatures there are with not a one left out— frail or firm, long or large, medium, small, tiny or round, seen or unseen, living far or near, those who have been born and those about to be born— may all beings be happy!
Let none deceive another, nor look down on anyone anywhere. Though provoked or aggrieved, let them not wish pain on each other.
Even as a mother would protect with her life her child, her only child, so too for all creatures unfold a boundless heart.
With love for the whole world, unfold a boundless heart: above, below, all round, unconstricted, without enmity or foe.
When standing, walking, sitting, or lying down while yet unweary, keep this ever in mind; for this, they say, is a divine meditation in this life.
In plainer words
Whoever wants to reach peace should be capable and straight, easy to talk to, gentle, not full of themselves, content, not making work for others, living lightly. May everyone be happy and safe — every living thing without a single exception: big, small, tiny, seen, unseen, near, far, already born or not yet born. Nobody should deceive or look down on anybody. Even when provoked, do not wish harm back. The way a mother would put her own body between her only child and danger — hold everything alive like that. Standing, walking, sitting, lying down, hold it. They call this the divine way to live here.
A restatement in modern English, written for this collection. The passage above is the text; this is one way of putting it.