I agree 100% - the gospel of John is probably the most critical book in the NT - no, not saying the others are unimportant or anything, but there are ALOT of NITTY GRITTY details in it that will more than help you grasp an understanding of not only the gospel, but the rest of the NT as well.
For example - there are even the most detailed of verses in there that if you catch them, it will help you grasp a big understanding of the bigger concepts et al.
For example -
Joh 6:39 And this is the Father's will which hath sent me, that of all which he hath given me I should lose nothing, but should raise it up again at the last day.
Joh 6:40 And this is the will of him that sent me, that every one which seeth the Son, and believeth on him, may have everlasting life: and I will raise him up at the last day.
John 6:54 Whoso eateth my flesh, and drinketh my blood, hath eternal life; and I will raise him up at the last day.
The key words in these verses are LAST DAY - just looking at the words in these 3 verses, it all but DEBUNKS this pre-tribulation rapture that alot of our modern day "bible teachers" like Tim LaHaye, Jerry Jenkins, Hal Lindsey, Joel Rosenberg, Grant Jeffries, etc, etc try to ram down everyone's throat and make $$$$ off of.
Of course, there's plenty of other scripture debunking the pre-trib rapture, but these verses alone saying how we'll be raised up on THE LAST DAY...