Here a few of my research conclusions based on a few writings of conservative Bible scholars.

If you have a question about God and know nothing about Him or the Bible...
START with the APOSTLE / DISCIPLE / "most beloved of Jesus"
...John the Elder, Son of Zebedee...his gospel and his letters!

REFs:

www.earlychristianwritings.com/john.html

bible.org/seriespage/gospel-john-introdu...

Most scholars date this gospel c. 90s-100.
There is a growing number of scholars, however, who place it sometime before the destruction of Jerusalem in 70 CE.
 John still would be the last gospel penned, even though it would not have been written until c. 65.
There is much primitive terminology used in this gospel. E.g., Jesus’ followers are called “disciples” in John, not apostles.
As with the other gospels, no MSS which contain John’s Gospel affirm authorship by anyone other than John.
...from the beginning of the second century, the fourth gospel was strongly attached to the apostle John.
..."P"—the earliest fragment for any NT book—contains portions of John 18:31-33 and 37-38
and is to be dated as early as 100 CE;
and the Papyrus Egerton ,
which is to be dated at about the same time, draws on both John and synoptics for its material.
...The oldest fragment of the New Testament, known as "P" or the John Rylands fragment,
attests to canonical John and is dated paleographically c. 120-130 CE.
Early external testimony places the publication of this gospel in Ephesus.
There is also some testimony that John the apostle lived out his later years in Ephesus.
John’s Gospel places an emphasis on the deity of Christ more explicitly than any other gospel.
John presents Jesus as the Christ, the Son of God, who is to be believed in order that one might right NOW pass from "death" to "life".
John’s Gospel was written at about the same time as Matthew and Luke,
for the evangelist shows virtually no awareness of the material found in the other gospels (typically common oral traditions being an exception).

WHY written:
John wanted to give Paul’s churches the gospel because Paul died.
He wrote the last chapter in haste, and as the final catalyst to his efforts, because Peter died.
...after the death of Paul (summer of 64), the remaining apostles felt it necessary to communicate to Paul’s churches
in order to make sure that they knew how they felt about Paul’s gospel.
Peter wrote one letter, then another.
John was putting on the finishing touches of his gospel for Paul’s churches (
since the churches of Asia Minor had none and since Paul did not know Christ according to the flesh) when Peter was arrested.
John had intended merely to end the gospel at chapter 20, as seems obvious.
What made him add the final chapter?
2 Peter 1:15 gives the clue:
“Now I am eager that each of you have a memorial of these things after my departure.”
This verse has been interpreted in many ways, but whatever it refers to it is fairly clear
that some sort of posthumous document written by other than Peter is in mind.
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Unique Theology of John's Gospel
...For the Gospel of John set the new religion upon the rails of thought and theology upon which it was to run for a thousand years.
The Greeks called it the Gospel of John the Divine —the Theologian—as we speak of the "Great Divines."
So clearly did they recognize this great quality in it...
...John never mentions the church or its officers, but no gospel lays more stress on both....
....While the church is never mentioned in John,
it is symbolized in Jesus' circle of personal followers and in the group of disciples in the Upper Room Discourse, chapters 13 and following.
...The Gospel of John is a charter of Christian experience.
For the evangelist, to know Christ through inner experience matters more than to have seen him face to face in Galilee.
"Blessed be those who believe without having seen me," 20:29.
What supremely matters in religion is not so much what men said or did, here or there,
but the power of the Christian experience to create itself anew in the human heart, no matter where or when.
...There is something almost liturgical in sentences using the great " I AM's "...before Abraham was " I AM ".
"I am the Bread that gives life," "I am the Good Shepherd," "I am the Door," "I am the Light of the World,"
"I am Resurrection and Life," "I am the Way and the Truth and the Life." They are in the religious style of the mystery religions.
Without that what would all the dogmas, all the liturgies, and all the literatures be worth to us?
John's difference from the other gospel narratives was recognized by such ancient Christian writers
such as Clement of Alexandria in the late second century,
Origen in the early third century, and
Eusebius in the early fourth century,
who set the stage for opposing views of John's relation to the Synoptics.
John was deemed either compatible with, if supplementary to, the other canonical Gospels,
as Clement and Eusebius believed,
or obviously at odds historically with the companion works, according to Origen’s opposing view. ..
From the time of Irenaeus (A.D. 180-89) certainly,
and probably from the time of the making of the Fourfold Gospel corpus (115-25),
the name of John has been attached to the gospel,
doubtless from the fact that John the Elder was the writer of II and III John and very probably of I John, also.
The question of the identity and personality of John the Elder belongs, however, to the discussion of the Johannine letters.