#1 Sweeper keeper
To build a team around the philosophy of positional play, all 11 players must be adept with the ball, including the goalkeeper. Before Guardiola, few managers paid attention to the importance of including the goalkeeper into possession plays, directly writing that position off as "high-risk". Few had the courage to think how their goalkeeper can act as a third centre-back and relieve the team from pressure, leading to an easier path towards the opposition's goal.
Moreover, the duties of the goalkeeper is to sweep the loose balls, hence the name 'Sweeper Keeper.' To sweep means to rush out of goal whenever a long ball beats the defence line. The goalkeeper acts as a cushion to further frustrate the opposition and provide a sense of defensive solidarity at the back even with the team playing a high defensive line, up to 40 meters away from goal. Valdes, Neuer, and Ederson are considered a perfect fit for the Sweeper Keeper profile, and that's the reason Pep believed in them so much.
Conclusion
Currently, Manchester City sit atop the Premier League with 11 points difference ahead of arch-rivals Manchester United. The performance they are putting in each weekend is unbelievable, having recently achieved their 15th straight win in the toughest league of all times. Some said that Guardiola's way wouldn't work in England, where are the critics now? Some even turned into admirers.
The argument that Guardiola takes over "ready" teams are extremely false and any individual with a toddler-level football knowledge knows that. Pep changes the way a team plays when he takes over. He gives them an identity, solidarity, knowledge, and an exquisitely pleasing style of play. Just as Xabi Alonso said, "With Pep, it felt like having an MBA in Football."