Absorb Spell (Su) is a class feature of the Spellthief (Complete Adventurer variant, p. 13) and it reads as follow:
Beginning at 7th level, if a spellthief makes a successful save against a spell that targets him, he can attempt to absorb the spell energy for later use. This ability affects only spells that have the spellthief as a target, not effect or area spells. A spellthief can't absorb a spell of a higher spell level than he could steal with his steal spell ability (see above).
To absorb a spell that targets him, a spellthief must succeed on a level check (1d20 + spellthief class level) against a DC of 10 + the spell's caster level. Failure indicates that the spell has its normal effect. Success means that the spellthief suffers no effect from the spell and can cast the spell later (or use its energy to cast one of his own spells known) as if he had stolen the spell with his steal spell ability. His normal limit of total spell levels stolen still applies.
At 20th level or higher, a spellthief can choose to use the stolen spell energy as an immediate action (see page 137), either to recast the original spell or to cast one of his own spells known using the stolen spell energy.
Let me pick these two phrases:
- if a spellthief makes a successful save against a spell that targets him, he can attempt to absorb the spell energy.
- To absorb a spell that targets him, a spellthief must succeed on a level check.
So, in order to absorb the spell, you must succeed on a saving throw and then pass the level check.
What I do not understand is this part:
Failure [on the level check] indicates that the spell has its normal effect.
Does it refer to the fact that the spell completely affects you even after a successful save?
Does it mean that if the spell's descriptor has something like "Saving Throw: Reflex half" then this halved damage (or effect) still applies?