As a child of the streets of London, unloved with no one to care for him, and as a man who was once married to a termagant who threatened to kill their child, a child whom he has not seen for many, many years, Provis feels that he finally has someone to love, someone to whom he can be like a father and to whom he can give his property. With this one love Provis has found solace in his life as well as value. For, if his money turns Pip into a gentleman, does not he, Magwitch/Provis, not, then, have some worth?
Provis is proud to tell Pip,
"Yes, Pip, dear boy, I've made a gentlman on you! It's me wot has done it!...Do I tell it fur you to feel a obligation? Not a bit. I tell it fur you to know as that there hunted dog wot you kept life in got his head so high that he could make a gentleman--and, Pip, you're him!"
I think that you can see why Magwitch says this if you just look at the words he uses in this chapter. He says to Pip that
I've come to the old country fur to see my gentleman spend his money like a gentleman. That'll be my pleasure. My pleasure 'ull be fur to see him do it.
What he is saying is that Pip is "his" gentleman and it will be fun for him to watch Pip spend the money.
The reason that he feels this way, of course, is the fact that it is his money that has made Pip into a gentleman. Magwitch is the convict that Pip helped way back at the beginning of the book and it is he who has arranged to have Pip made into a gentleman. Pip does not know this at this point in the novel, of course.
So Magwitch is going to get great pleasure because he wanted Pip to become a gentleman. In that sort of a situation, you can see why he would want to get to actually see the results of his efforts.