As for a summary of the document, this has already been covered but no quotes from the text have been provided up to this point. Of course, one of the most widely known verses in the Gospel of John is John 3:16 which does not need to be repeated here because any Christian would know it. Other notable passages include chapter 18 when Jesus is arrested, the raising of Lazarus in chapter 11 and the feeding of the five thousand in chapter six. Actual quotes that are noteworthy include John 6:20, when Jesus is walking on the water, when he says "It is I…do not be afraid." Another one to point to is John 3:18, which obviously is just after John 3:16, but is the verse that notes that whomever is believed is not condemned. One set of passages and events that is NOT covered in John is the birth of Jesus and the travails of Mary and Joseph.
As for modern impacts in today's society, there is a wide amount of perspectives and viewpoints about the Bible that are wildly different one to another. Some churches say that being rich is the root of evil while others are on the complete other side and suggest that there is nothing wrong with being rich and they point to people like King David. Some suggest that one must live a very pious live to get into Heaven while others state that so long as one believes in God and Jesus (as noted in the third chapter of John),...
The Jewish faith and other Bible-related faiths that center on any part of the Bible don't believe Hell even exists or suggest that there is an intermediate step in between Earth and Heaven. Examples of this belief structure include the Jews and the Catholic Church.
Conclusion
In the end, the Gospel of John in many way mirrors the other Gospels but it's definitely different enough from the other Gospels to matter and can certainly stand on its own as a historically and cultural relevant document that many people can and should point to as it relates to the Christian faith. While it may not be the focus of (or a main one, anyway) of the Jews and other Old Testament churches, it is still certainly worth of review. The cultural impacts and developments of the Gospel of John are certainly not hard to see and it's obvious that the book is being interpreted and followed quite differently from church to church. Barring a seismic shift in the church or new learned knowledge about the Bible, the disparate nature of the Christian church that started with the Pharisees and continues today will probably not change much.
References
Holy Bible: New Interntaional Version. (2011). (NIV church Bible ed.). Grand Rapids, Mich.: Zondervan.
