In Chapter 21 of The Giver, when Jonas decides to take Gabe with him, but why did he choose to ride a bike instead of using the Giver's car?
And, when Jonas did escape, why didn't his memories flow into the Community? How would the community have gotten the memories if Jonas didn't die?
Jonas did not take the Giver’s car because he had to escape early, and The Giver would not be able to leave while he was missing.
One of the reasons Jonas escapes with the bicycle is that it is handy. His father’s bike is at their house, whereas he would have to go elsewhere to use the car. To escape by hiding in the car would require waiting until The Giver left. Since Jonas would likely be discovered to be missing before The Giver had a chance to leave, hiding in his car for all of that time would be risky. Time was of the essence.
There was no time. Every minute counted now, and every minute must take him farther from the community. (Ch. 22, p. 163)
Another reason he uses the bicycle is because he does not know how to drive a car. Notice that The Giver was planning to have a driver.
… The Giver would order a vehicle and driver from the Speaker. He visited the other communities frequently, meeting with their Elders; his responsibilities extended over all the surrounding areas. … The Giver would help Jonas hide in the storage area of the vehicle. (Ch. 21, p. 160)
This plan would only work if Jonas was not discovered. Even if they ignored Jonas’s absence, no one would ignore Gabe’s. The minute Jonas decided to take Gabe, the old plan would not work. He had to flee with the baby, and he had to do it early. He could not use any of The Giver’s help, because there was no way The Giver could help him and no time to wait for help anyway.
Lowry, Lois (1993-04-26). The Giver (Newbery Medal Book). Houghton Mifflin Harcourt. Kindle Edition.