La Roja finished behind Argentina and Colombia in the South American qualifying group and play Brazil next week as preparations for the 2014 finals gather pace.
Even if England boss Roy Hodgson opts to tinker with his line-up, Sampaoli will be taking the contest, and next week's clash with the Samba Boys, seriously.
Sampaoli said: "It's very, very important as part of our preparation. These next two friendly games, against top world sides like Brazil and England, will give us an idea of where we are and how we're going to compete in the World Cup.
"We know those two sides are going to give us a real stiff test and that's important for us.
"Any mistakes you make, they don't let you off. For me, the World Cup starts on Friday.
"Irrespective what the line-up is, it's important we hit our straps and treat it like it's the World Cup. It's a competitive match for us."
Chile memorably beat England 2-0 in February 1998 with two goals from Marcelo Salas, the current team's guest of honour this week.
The South Americans went on to reach the last 16 at France 98, losing to eventual runners-up Brazil, and Sampaoli knows the importance of facing European opposition ahead of next summer's tournament.
"We know it's an important fixture for us, to come here and play England at home," Sampaoli added.
"England are always considered one of the top sides in the world in the FIFA rankings and are particularly strong when they play at home.
"We know that it's a challenge for us, but we've got to try to impose our style of play on the game tomorrow night.
"We will try to take advantage of the breakdowns in play, the transitions in play and try to attack on the counter.
"We will, for sure, be drawn against a European side in the World Cup finals, so it is important to see how we measure up."
England laboured through their World Cup qualifying group before beating Montenegro and Poland to secure their progress to the finals.
There have been numerous critics of Hodgson's England, but Sampaoli is not among them.
"The manager has got them quite disciplined and they're a strong unit defensively and keep things tight," he said.
"At the same time, any breakdowns in play on the counter they're very, very quick to break out.
"When you've got (Danny) Welbeck fit and with the likes of (Wayne) Rooney and (Daniel) Sturridge, they create lots of problems and can make life very complicated for opposition defenders.
"They showed that in the game against Brazil, the two goals against Brazil.
"They're a good side with a good chance (at the World Cup). What they've got to do is make sure they create enough of a goal threat to cement those good chances.
"They are a team that will get stronger during a tournament. They will get better and better as they progress."
Chile are likely to be without two of their more influential players.
Juventus midfielder Arturo Vidal is out with a calf strain, while Palmeiras' Jorge Valdivia faces a late fitness test to determine whether he can play at Wembley.
The attacking threat is led by Alexis Sanchez of Barcelona while Cardiff midfielder Gary Medel will have a key role to play, too, and has impressed his national team boss since moving to the Premier League from Sevilla.
Sampaoli said: "I've been monitoring Gary's progress and he has settled in really quickly. I think that is down to his ability and his aggression. He is a decent player and will be recognised for those qualities as time goes on with his club.
"He may be playing a more defensive role with us compared to his club.
"We rely on him for his physical presence and his strength is a marker in midfield rather than being creative. He is an important figure for us."
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