Why does insight lead to to compassion?

Process of insight up roots Loba, Dosa, Moha 1st and hence as you practice you are left with more Aloba, Adosa, Amoha and Ahetuka states of mind. In addition 5 hindrances also fall away of which ill will is diminishments cases more competition.

When liberated you are left Ahetuka but still evil roots are no more hence relatively compassionate with someone who has ill will and the evil roots.

Isn't compassion just a byproduct of the selflessness or egolessness that is a byproduct of a lot of insight?

"insight" typically is a short-hand way of saying "insight into the true nature of Reality" or "insight into the true nature of our situation"

So if insight (by meditating on selflessness, for example) leads one to see definitively, directly, and intuitively that there is no separate self, then the aims of the many and the aims of the nominal "individual" are seen as overlapping to say the least.

So what's the real condition? In a sentence, all sentient beings want happiness / freedom from suffering. They don't wish to suffer, they wish to be happy.

Insight can lead to an experiential understanding of this, which is where insight into selflessness of all dharmas yields its fruit so-to-speak.

Selflessness can be demonstrated by various shapes of reasoning. The computer monitor you see is not really "a computer monitor" because it's made of many separate parts. Each part is itself not a computer monitor, you have the shell, the screen, the stand, the cable. The shell is not a monitor, the stand is not a monitor, etc. So where is the monitor?

Similarly, we can apply this clear and logical reasoning to a separate, independent, lasting self and see that truly no phenomenon has self-ity. Some might jump to the conclusion and say "well then everything is one!" but that is also excess talk. One is a word that comes up in dependence on the concept of Many and, therefore as dependent upon each other, neither one exists nor not-exists in the middle free of extremes.

The logical part must always be supported by and footed in the understanding that we don't want to suffer. From the largest man to the smallest insect, from the whales to the birds, all beings are day-and-night avoiding pain (or perceived pain) and working toward happiness (or the skewed cultural reinforcement of what happiness should look like).

Insight into the situation gives us compassion, which is a fundamental aspect of clarity. Much like a person watching the inner workings of a clock, when we see the cyclic functioning of samsara, we feel for the beings who are trapped in unwholesome cycles. Furthermore, the only separation between us and other beings is really just our karmic histories/trajectories. Had we accomplished the same deeds and thoughts as other beings we would be on their exact paths, and thus knowing that we could just as easily be in switched places with others is another key element in understanding selflessness, which in turn gives the incipient awareness of true compassion.

Compassion (yearning for and acting for the end of all beings' sufferings) and Wisdom (that realizes emptiness) are what makes a Buddha.

When you begin to see the interdependence and interconnectedness of all beings through meditation you will also begin to see that we all suffer. Naturally you do not want to suffer yourself, and see that others are suffering too, this begins to arise some compassion for 'their' sufferings... that's all.

1 When our ignorance is removed, our suffering ends.

2 When our suffering ends, the true nature of things is known.

3 When the true nature of things is known, the true nature of beings is known.

4 When the true nature of beings is known, the cause of suffering in beings is known.

5 When the cause of suffering in beings is known, the strive of beings to end suffering is clearly seen.

6 When the strive of beings to end suffering is clearly seen, our compassion for all beings arises.

Through the practice of insight hate is reduced, craving is reduced and the 4 Brahma Viharas develops as a result of those reduction, i.e Metta(loving kindness), Karuna (compassion), Mudita (joy in the joy of others) and Upekkha ( Equnamity).

Now the far enemies of the 4 Brahma Viharas are:

• Metta - ill-will
• Karuna - cruelty
• Mudita - Envy
• Upekkha - Craving/Aversion

And through the insight practice of reducing hate and craving, ill-will is reduced, good-will increases; cruelty is reduced, harmlessness increases, envy is reduced, sympathetic joy increases, craving/aversion is reduced equanimity increases.

Compassion was more highly praised by the Buddha:

because it is the root of so many other virtues. The Jàtakamàlà says, ‘Compassion gives birth to all the other virtues just as cooling rain makes the crops grow. When a person is compassionate he has no desire to harm his neighbour, his body, speech and mind are purified, concern for one’s neighbour’s welfare increases and states like kindness, patience, happiness and good reputation grow. Being calm, the compassionate person does not arouse fear in the minds’ of others, he is trusted like a kinsman, he is not agitated by the passions, and quenched by the waters of compassion, the fire of hatred does not blaze in his heart…Remembering this strive to develop compassion towards others, as if they were yourself or your offspring.’