In the opening scene, Edmond is present when Gloucester, talking to Kent, makes crude references to his conception and birth. He publicly reacts as expected.
In scene 2, in a soliloquy, Edmond tells us how he really feels. He appeals to Nature as his goddess. Exactly what does he mean? When most people think of nature, they think of positive nature, flowers, trees, furry little animals, etc. Edmond is not appealing to those forces of nature. Rather he is talking to the negative power of nature.
In his world, he is marginalized due to circumstances beyond his control. That his mother was not married to Gloucester is not his fault yet society labels him a bastard.
When he compares himself to his brother, he discovers that physically and mentally they are alike. It is not as if he was born with a B branded on his forehead, yet in his world it exits none the less.
He takes comfort in the fact that at least there was fun in his illegitimate conception as compared to the duty performed in legitimate conception.
He justifies his betrayal of his brother and his father.
"Now gods, stand up for bastards!"
Your question refers to Edmund's opening speech in act1 sc.2 of King Lear. This solo speech holds the crucial key to Edmund's character, his advocacy of 'Nature' by virtue of being a natural child, a bastard, of Gloucester. Because of being born out of wedlock, he is illegitimate and marginalised as per social convention. Gloucester's legitimate son, Edgar, is due to enjoy all property rights, and Edmund is destined to be neglected and deprived.
In this speech, Edmund raises questions against social stgmatisation of the bastards, for no faults of theirs. He is as well-shaped in body and mind as all other legitimates in the world, and yet he is set aside as base:
Why bastard? Wherefore base?
When my dimensions are as well compact,
My mind as generous, and my shape as true,
As honest madam's issue? Why brand they us
With base? With baseness? Bastardy? Base? Base?
Edmund banters at Edgar's 'legitimacy', and ventilates his grudging anguish for discriminations against the so-called bastards. Since he is a 'natural' child, he vows to go by 'nature', to go by the principle of the 'survival of the fittest', not bothering for others, but only bothering to promote self-interest.