Why does Pip tell Magwitch about Estella?

Pip tells Magwitch about Estella because he is dying. He does this because he finally understands that it isn't all about social class and position...... it's about loyalty and love. This is why he puts Magwitch's mind at ease....

“Dear Magwitch, I must tell you, now at last. You understand what I say?”

A gentle pressure on my hand.

“You had a child once, whom you loved and lost.”

A stronger pressure on my hand.

“She lived and found powerful friends. She is living now. She is a lady and very beautiful. And I love her!”