Since you ignored my analogy of the Christmas gift (I'd still like an answer to that), I'll use yours. If you had an adopted son and he disobeyed you, would you reject him and kick him out of the family or just discipline him to teach him the right way? The RC way, making the gift of sonship at all conditional on obedience, means he is out of the family.
Disobeyed? no. Disinherited himself (as with the prodigal son)? It would not be by my choice. That parable takes on more meaning the deeper you take it in this discussion, but the "once saved, always saved" thread has been well fleshed out by both sides on previous threads.
If the obedience, in and of itself, cannot merit Heaven... how can the disobedience (after accepting Christ) merit Hell? Only the rejection of Christ (the disinheriting) could do that and the Spirit guards us against that choice.
By the way, I didn't mean to ignore your Christmas present analogy (I could really use a DVD player if you're still shopping), I agree that it is true...I just didn't see it as terribly on point. The obedience does not merit the free gift... it is a response to it.