Short answer: From an evangelical Christian perspective, the most likely author of the words in John 15:5 and 15:8 is the Apostle John—commonly identified with “the disciple whom Jesus loved” and traditionally understood to be the eyewitness writer of the Fourth Gospel.

Why evangelicals identify John the Apostle as the author
– Internal testimony: The Gospel itself points to an eyewitness author (e.g., John 21:24: “This is the disciple who testifies to these things and who wrote them down”). The unnamed “beloved disciple” is traditionally equated with John the son of Zebedee.
– Early church testimony: Early Christian leaders close to the apostolic age (Papias, Irenaeus, Clement of Alexandria, and others) unanimously attributed the Gospel to John the Apostle, who is said to have lived and written from Ephesus.
– Eyewitness detail and theological tone: Evangelicals argue the Gospel’s vivid, intimate details of Jesus’ life and the high Christology (the “I am” sayings, strong emphasis on believing, abiding, and eternal life) fit an apostolic eyewitness who had close fellowship with Jesus.

Who John the Apostle was (brief bio highlights)
– Son of Zebedee and brother of James, a fisherman called by Jesus (Mark 1:19–20).
– Part of Jesus’ inner circle (Peter, James, John); present at the Transfiguration, the raising of Jairus’s daughter, and at the cross (John 19:26–27).
– Traditionally thought to have ministered in Ephesus and to have lived into old age, giving him opportunity to write (the Gospel, three epistles, and—according to many evangelicals—Revelation).

How authorship relates to John 15:5, 8
– John 15 echoes central Johannine themes: intimate union with Christ (“abide in me”), the necessity of faith and relationship for spiritual life, and fruitfulness as the evidence of true discipleship.
– From an evangelical perspective, because John is seen as an eyewitness and theologically reflective apostle, these verses are treated as authoritative teaching about the believer’s union with Christ, the nature of Christian fruitfulness, and how our lives glorify the Father.

Evangelical convictions about the significance
– The Gospel is inspired, historically reliable, and intended to lead readers to faith (see John 20:30–31).
– The metaphor in John 15 is practical: abiding in Christ produces spiritual fruit that testifies to genuine discipleship and brings glory to God—central concerns in evangelical teaching on discipleship and sanctification.

A note about alternative scholarship
– Some critical scholars propose a later “Johannine community” or an anonymous author editing eyewitness traditions. Evangelicals generally give greatest weight to the early patristic testimony and the Gospel’s own claims, affirming Johannine authorship while still engaging critical scholarship.

If you’d like, I can:
– Summarize how John’s life and background shed light on specific words or phrases in John 15:5, 8;
– Provide short devotional reflections or preaching points on these verses from a traditional evangelical perspective.