Why is it said that the position of the Whip is important in the parliamentary system?

A Whip is a member of parliament who makes sure that other members of his party are present at voting time and that they vote in a certain way. The Whip ensures that members of the party are present in sufficient numbers in parliament. It is his job to make sure that they vote according to the line taken by the party on important questions. The Chief Whip of the government party is the minister of parliamentary affairs. He is answerable to the leader of the house.

 The whips of the ruling party and of the opposition keep in constant touch with each other. Whips are of three types one-line, two-line and three line whips. The number of lines indicates the importance attached to a particular measure before the house.