This is to be done by one skilled in aims
appreciating the state of peace:
Be capable, upright, & straightforward,
easy to instruct, gentle, & not conceited,
content & easy to support,
with few duties, living lightly,
with peaceful faculties, astute,
modest, & no greed for supporters.
Do not do the slightest thing
that the observant would later censure.
Think: Happy, at rest,
may all beings be happy at heart.
Whatever beings there may be—
weak or strong, without exception,
seen & unseen,
living near & far away,
born or seeking birth:
May all beings be happy at heart.
Let no one deceive another
or despise anyone anywhere,
or through anger or resistance-perception
wish for another to suffer.
As a Mother would risk her life
to Protect her child, her only child,
even so should one cultivate the heart limitlessly
with regard to all beings.1
With Goodwill for the entire cosmos,
cultivate the heart limitlessly:
above, below, & all around,
unobstructed, without hostility or hate.
Whether standing, walking,
sitting, or lying down,
as long as one has banished torpor,
one should be resolved on this mindfulness.2
This is called a Brahmā abiding
Not taken with views,
but virtuous & consummate in vision,
having subdued greed for sensuality,
one never again
will lie in the womb.
The image here is sometimes misconstrued as saying that one should protect all beings as a mother would protect her only child. Actually, the parallel is not between the child and all living beings; it is between the child and one’s cultivation of the heart: One should protect one’s goodwill toward all beings in the same way that a mother would protect her only child. On this point, see MN 21.
This line has to be read in line with the Buddha’s definition of mindfulness as the ability to keep something in mind. See SN 48:10.
See also: MN 52; MN 97; MN 135; SN 42:8; SN 46:54; SN 55:7; AN 3:66; AN 4:67; AN 4:96; AN 4:125–126; AN 4:178; AN 4:200; AN 5:20; AN 5:27; AN 6:12–13; AN 8:70; AN 10:176; AN 10:196; AN 11:16; Ud 5:1; Iti 22; Iti 27
from Buddhism https://www.reddit.com/r/Buddhism/comments/9ps13h/khp_9_karaṇīya_mettā_sutta_goodwill/