I understnad that you have always been told that this passage means something that the actual language of the passage cannot mean gramatically.
Its a matter of grammar. Because you are wedded to a certain theology you have invented a grammar that you apply only to this passage of scripture in order to force it to mean something not present in the actual words - and that would never ever apply to any other sentence.
Lets take two sentences:
1. "God gave us the bible so that we might be thoroughly perfect."
2. "Dad gave us the pistol so that we would be thoroughly safe from harm."
#1 represents the scripture in question and its actual grammar. #2 is a grammatical analogue.
Dad gave us the pistol so we would be safe from harm - but that does not imply that he gave us nothing else so that would be safe. It is silent as to anything else he may have given us to be safe in addition to giving us the pistol. But even here, it is clear that Dad gave us safety and shooting lessons at some point so that we would know how to use the pistol - otherwise it actually decreases our safety since we have no idea how to handle it or use it for its intended purpose.
This is all straightforward. The grammar clearly does not rule out dad having given us other things (like the shooting lessons, a radio or a knife) that would also contribute to our complete safety.
So too with the grammar in #1 - it is silent as to anything else God may have given us in addition to scripture to help us be totally perfect - it does not rule out that God may have provided other things that also help us to be totally perfect.
It is not a matter of grammar - it is a matter of
meaning. You are (in addition to making unwarranted ad hominem attacks on me claiming I am inventing a grammar, which I am plainly not doing) arguing that "perfect" does not mean "perfect". Let me give you a couple definitions from Websters:
1. Lacking nothing essential to the whole; complete of its nature or kind.
2. Being without defect or blemish.
If I am wholly complete, without defect or blemish by scripture, what else could I possibly need? There is nothing else you can add to make me any more complete - that is impossible, as I am already fully complete. Therefore, there is nothing besides scripture that can make me more perfect. If you add something to perfection it becomes imperfect.
Your comparison between the two sentences is invalid because you are comparing perfection with imperfection.