Confusion about using scrolls for higher level spells

[LucyG92]

If you want to use a scroll that has a spell on your class spell list and have the appropriate ability score, but you're not high enough level to cast it, do you have to make a 'caster level' check rather than use magic device? For example, my level 5 sorceress has a scroll of Deep Slumber - spell level 3. A wizard would have to be level 5 to cast that, sorcerer level 6. What's the DC for this (6?) and what check do I need to make? Sorry, I've gotten myself really confused about this. :)

[Gilfalas]

PFSRD wrote:

To have any chance of activating a scroll spell, the scroll user must meet the following requirements.

The spell must be of the correct type (arcane or divine). Arcane spellcasters (wizards, sorcerers, and bards) can only use scrolls containing arcane spells, and divine spellcasters (clerics, druids, paladins, and rangers) can only use scrolls containing divine spells. (The type of scroll a character creates is also determined by his class.)
The user must have the spell on her class list.
The user must have the requisite ability score.

If the user meets all the requirements noted above, and her caster level is at least equal to the spell's caster level, she can automatically activate the spell without a check. If she meets all three requirements but her own caster level is lower than the scroll spell's caster level, then she has to make a caster level check (DC = scroll's caster level + 1) to cast the spell successfully. If she fails, she must make a DC 5 Wisdom check to avoid a scroll mishap. A natural roll of 1 always fails, whatever the modifiers. Activating a scroll is a standard action (or the spell's casting time, whichever is longer) and it provokes attacks of opportunity exactly as casting a spell does. If the caster level check fails but no mishap occurs, the scroll is not expended.

The above is from the scrolls section of the magic item rules.

[LucyG92]

I am a little confused though, I thought this was exactly what Use Magic Device is for?

[Rysky]

If you're using a Scroll normally, the DC is Caster Level +1.

If you use UMD, the DC is Caster Level + 20

[Quintessentially Me]

Also, philosophically UMD is intended for those times when you are using "alien" magic i.e. magic that you are not already trained to use. Note that UMD is required for casting a spell from a scroll when the spell is not on any of your spell lists. Moreover, that you can cast a spell that is on one of your spell lists from a scroll without a UMD check.

So the caster level check is not because you are using "alien" magic; that is handled by UMD. The caster level check is because you are attempting magic you do understand but that is over your normal power level.