Wemmick played an important role in Pip’s life by giving him advice, but he was careful about how he did it because he liked to keep his work life separate from his home life.

When Pip leaves his home to go to London, he has a guardian on paper, but really doesn’t have anyone to play the role for him emotionally.  The person who came the closest to giving Pip advice was Wemmick, although he was very careful about how did it.

In Pip's life and in the book, Wemmick serves as a contrast to Jaggers, the cold and harsh lawyer.  While Wemmick seems on the surface as cold and harsh as Jaggers, he has a softer side that he reveals only to Pip and a few others.

Wemmick was a very private person.  He liked to keep his work persona separate from his home persona.  At work, he was a strict person who believed in taking what he could get and hanging on to it, and he passed those lessons on to Pip in a businesslike way.

“Oh yes,” he returned, “these are all gifts of that kind. One brings another, you see; that's the way of it. I always take 'em. ... They may not be worth much, but, after all, they're property and portable. [My] guiding-star always is, Get hold of portable property.” (Ch. 24)

Wemmick is not the most loveable guy when he is at work with Pip, but when he takes Pip home, his manner changes.  Actually, it changes on the way home.  To Wemmick, it is important that Jaggers does not know about his home life.  He wants to keep these two parts of himself separate, as if the darkness of the office would infect the innocence of the home.

At home, Wemmick is whimsical and nurturing.  This is a complete contrast from the harsh and no-nonsense Wemmick he is at Jaggers’ office.  He takes care of his elderly father, the Aged Parent, and even has a sweetheart named Miss Skiffins.

Wemmick’s house looks like a castle, complete with a gun that fires.  When he brings Pip home to visit, he is showing him a great deal of trust, letting him see this other side of himself.

I expressed the readiness I felt, and we went into the castle. There, we found, sitting by a fire, a very old man in a flannel coat: clean, cheerful, comfortable, and well cared for, but intensely deaf. (Ch. 25)

This is a complete contrast with Jaggers’s house, which is as harsh and overbearing inside and out as the man inside.  Jaggers also behaves this way, treating Molly, his servant, roughly and pointing out that he can dominate her.  

Her entrapped hand was on the table, but she had already put her other hand behind her waist. “Master,” she said, in a low voice, with her eyes attentively and entreatingly fixed upon him, “Don't.” (Ch. 36)

Both men’s houses and behavior in them represent their true natures.  Wemmick is gentle and caring, and Jaggers is harsh and abusive.

Jaggers never gives Pip any real advice except for legal advice.  He tells him what he can and cannot do, such as how much money he has.  He does show some interest in the fact that Pip is running through a lot of money, but never really any guidance.  He does advise him on legal matters when Magwitch appears, but is not able to keep the man alive (though that might have been a futile task, with his enemy Compeyson after him).

Wemmick, on the other hand, invites Pip to his wedding.  He gives Pip advice about putting Herbert into business (though he does not take it).

“Choose your bridge, Mr. Pip,” returned Wemmick, “and take a walk upon your bridge, and pitch your money into the Thames over the centre arch of your bridge, and you know the end of it. Serve a friend with it, and you may know the end of it too—but it's a less pleasant and profitable end.” (Ch. 36)

While telling Pip that giving Herbert the money to put him into business was the same as throwing his money off of a bridge may not have been what Pip wanted to hear, it was advice, and it was Wemmick’s honest opinion. 

Wemmick was a good friend to Pip when he had few.  Herbert and Pip were pretty much clueless most of the time, and Jaggers had the philosophy to stay out of it, telling his young charge that he was his guardian in name only.  Wemmick saw a boy who was in over his head, and decided to make him a friend.  Pip would have been lonely and the book would have been much more one-sided without him.