From the Lonaphala Sutta:
Now, a trifling evil act done by what sort of individual is experienced in the here & now, and for the most part barely appears for a moment? There is the case where a certain individual is developed in the body, developed in virtue, developed in mind [i.e., painful feelings cannot invade the mind and stay there], developed in discernment: unrestricted, large-hearted, dwelling with the immeasurable. A trifling evil act done by this sort of individual is experienced in the here & now, and for the most part barely appears for a moment.
What developed in body and developed in mind means, is elaborated in MN36:
"And how is one developed in body and developed in mind? There is the case where a pleasant feeling arises in a well-educated disciple of the noble ones. On being touched by the pleasant feeling, he doesn't become impassioned with pleasure, and is not reduced to being impassioned with pleasure. His pleasant feeling ceases. With the cessation of the pleasant feeling there arises a painful feeling. On being touched with the painful feeling, he doesn't sorrow, grieve, or lament, beat his breast or becomes distraught. When that pleasant feeling had arisen in him, it didn't invade his mind and remain because of his development of the body. When that painful feeling had arisen in him, it didn't invade his mind and remain because of his development of the mind. This is how one is developed in body and developed in mind."
What being developed in virtue (sila) means, is covered by the Five Precepts (and also the Eight Precepts and Ten Precepts), Right Speech, Right Action and Right Livelihood. These links provide more info on these.
However, what does "developed in discernment" mean?
Please also provide references from the scriptures.