......

If you are lucky enough to get a sleeper, you spend half the night staring at the small blue light in the ceiling, or fumbling to find you ticket for inspection. Inevitably you arrive at your destination almost exhausted.

......

The journey is so smooth that there is nothing to prevent you from reading or sleeping. However you decide to spend your time, one thing is certain: you will arrive at your destination fresh and uncrumpled. You will not have to spend the next few days recovering from a long and arduous journey.

以上是新概念3-44：

请教老师：为什么“you arrive at your destination”用了一般现在时，没有使用will arrive ？

可是“you will arrive at your destination fresh and uncrumpled. You will not have to spend the next few days recovering from a long and arduous journey.”

却又分别使用了will arrive, will not have to spend 呢？并且However没有使用“逗号，”隔开？