Does this means that, as a ranger, you must keep the same spell selection during a whole level? Can't you change then after a long rest or something like that? A whole level seems too much time and gives little time for experimenting, right?

Yup. I'm okay with this -- actually, I prefer it.

Why? I started playing in 1E, when the Ranger had both Druid and Magic User (Wizard) spells. They were clearly not "nature/Druid Paladins". Instead, they were resourceful guys who learned some additional tricks. The Druid spells were really just there because the Magic User spells didn't provide the right tricks. It was a bit wonky to have two, completely separate spell lists, so I was fine with it being merged down to one, in 2E. Making them divine casters always rubbed me wrong, though. On the other hand, I didn't think it made a ton of sense to have them running around with big books, either.

So, fast-forward through a couple other variations of Ranger, to today. We've now got a history of arcane casters that just learn spells instead of preparing/memorizing them. Also, 5E doesn't really make a strong distinction between arcane and divine magic. Really, a given setting could say the Bard represented a "Knowledge Cleric" in the same way a Druid represents a "Nature Cleric" and there would be absolutely no mechanical issues with it, nor any rules fluff (as far as I recall) to contradict it.

So, in my games, I treat the Ranger as a soft-arcane caster (like the Bard) who happens to have some very woodsy-flavored spells. I do not want the Ranger's spells to look like the Paladin's. Working like the Bard is perfect.

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