act 4 Scene 1

Antonio offers to return his share of Shylock’s estate, on the condition that Shylock convert to Christianity and bequeath all his goods to Jessica and Lorenzo upon his death. Shylock consents and departs, saying simply, “I am not well” (IV.i.392). What could be worse the converting to Christianity in the eyes of a Jew?

He insists that Shylock's wealth go to Jessica and Lorenzo after his death.

I believe that in Shakespeare's time, converting Jews to Christianity was considered doing them a favor. Odd by our standards. Keep in mind also that if Shylock is Christian, he can no longer charge interest on his loans, since usury was a crime in the Christian world. Hence he will have no way to make money.