Why Apollo astronauts wore their suits during liftoff but removed them in the spacecraft

Why Apollo astronauts used to wear their suits during liftoff but they removed them in the spacecraft?Why they needed their suits during liftoff?
thanks

So when the rocket launches, it needs to break the force of Earth's gravity. When it shoots up to space, the astronauts feel extreme force and pressure called G-force. To protect them, they wear those suits.

Also, the temperature inside the rocket changes drastically as it rises higher and higher. nearly freezing in space.

In the spacecraft later on, they can take it off because temperature, pressure, etc is stablilized and no longer a threat.

David and Jonwook are full of it.
The "nick" answer is almost correct. In an emergency at high altitude, the Apollo astronauts might have had a low cabin pressure emergency. Shuttle astronauts might have needed to do an emergency escape out the hatch.
The USSR learned the hard way. Three cosmonauts were so crowded in a two man ship, they could not wear pressure suits. A loss of pressure killed them.

Have you actually watched a takeoff? Do you not see how utterly dangerous that scenario is. That rocket as big as a 747 only has to move a metre off vertical and all hell would let loose. The whole area is a colossal fireball.

The astronuats need a means of escape.

Cause they're cool lookin'