John followed the climactic proof that Jesus is God's Son with an explanation of his purpose for writing this narrative of Jesus' ministry. This explanation constitutes a preliminary conclusion to the book.
20:30 "Therefore"ties this statement to what immediately precedes it. John wrote his Gospel because those who believe on Jesus without seeing Him in the flesh are acceptable to God. He wrote, therefore, that people may believe and so enjoy eternal life. There were many other evidences of Jesus' deity that John could have presented. However, he chose those that he recorded here to lead his readers to the type of faith that Thomas just articulated and that Jesus just commended. That was John's strategy in composing this Gospel under the Holy Spirit's inspiration.
What did John have in mind when he referred to other "signs?"Perhaps he meant the seven miracles that he featured, the significance of which Jesus usually explained in the context (chs. 2-12).
It seems more probable that John meant to include the Resurrection since it was the greatest of all the demonstrations of Jesus' deity. Jesus explained the significance of this miracle in the Upper Room Discourse (chs. 13-16).
20:31 This verse unites many of the most important themes in the fourth Gospel. John's purpose was clearly evangelistic. His Gospel is an excellent portion of Scripture to give to an unbeliever. It is probably the most effective evangelistic tool available. Its impact on the reader is strongest when one reads it through at one sitting, which takes less than two hours for most people. This document can also deepen and establish the faith of any believer. However that is more a comment on its result than its purpose.
The implication of this purpose is that John meant unbelievers when he wrote "you."Did he have a particular group of unbelievers in mind, or was he addressing any reader? Some commentators have tried to identify a particular audience from statements in the text. Yet it seems more probable that John wrote for a general audience since he did not identify his intended audience specifically. His presentation of Jesus as the divine Son of God certainly has universal application.
"There cannot be any doubt but that John conceived of Jesus as the very incarnation of God."660
John's purpose was not academic. It was not simply that people might believe intellectually that Jesus is the divine Messiah. It was rather that they might believe those foundational truths so they could possess and experience the life of God fully (cf. 10:10). This divine life affects the whole person, not just the intellect. Moreover it affects him or her forever, not just during that person's present lifetime.
John's clear purpose statement concludes the body of this Gospel.
