The verb 'know' comes seven times in this final section. And the key verse that explains the purpose that John had in mind when he wrote this Epistle is : "I write these things to you who believe in the name of the Son of God, so that you may know that you have eternal life" (5:13). His Gospel was designed to help us into eternal life (John 20:31). This Epistle is to make sure we have experienced it.
Assurance is the certainty that God loves us, has accepted us into his family, and every sin and failure has been forgiven and forgotten. Many try to love and serve God without that assurance.
So in this summing up of the contents of the Epistle John repeats six strands of the assurance that he has already given us (4:16, 5:2, 13, 18, 19, 20).
4:16 Of the six assurances mentioned in the Introduction, the love of God is the first certainty that we have. The 'we' refers to John as one of the eye-witnesses (4:14).
4:17 And knowing this give us great boldness. Here "the day of judgment" does not refer to some final judgment that settles whether we go to hell or to heaven. It is the coming or parousia John was expecting very soon (as occured in AD 70, see 2:18, 28). And in our own situation it applies to the times of judgment we all expect in our personal, family, church, or national situations.
4:18 A gnawing fear is being afraid of being rejected and fairly or unfairly punished. But if we are assured of the love of God, "perfect love casts out fear."
4:19 This assurance of being loved is not something we invented. It originates in the love of God who loved us long before we ever thought of loving him.
4:20 But as we saw earlier, a genuine experience of God's parental love will make it impossible for us to hate our brothers and sisters in that family (see 2:9-11, 3:11, 4:7-12). .
4:21 This is the essence of the new commandment (2:8-11). And here the newness is in contrast to the invitation of faith set out in the Gospel (John 20:30-31).
5:1 Nicodemus was invited to be born again into the family of God (John 3:3, 7, see 1 John 2:29, 3:9). We are "begotten"as children of God but the Son is the "only begotten" Son of the Father. The evidence of new birth is a relationship both to Jesus as the Messiah and others who are born into the same family.
5:2 And we know this as we find ourselves loving the children of God whenever we love God, and obey his instructions.
5:3 This requirement of love is not in any way burdensome since it is given to us as part of the nature we receive as children of God.
5:4 And those who are born of God are also given the faith not to be defeated, or beaten down, or swallowed by the world around us (see 2:13, 14, 4:4, 1 Corinthians 15:57).
5:5 Faith can just be a direction of looking to the Light of the world (as in John 1:9, 3:19) without understanding what the Messiah has done. But an informed faith is believing that the Jesus who came and lived among us, as described in the Gospels, is in fact the eternal Son of God.
5:6 Jesus' ministry began with the water of his baptism. "This is my Son, the Beloved, with whom I am well pleased" (Matthew 3:17). And his ministry on earth ended with the blood of his cross. But it was the Spirit who worked in him from his baptism to the end (Luke 4:1, 14, 18), and then raised him from the dead (Romans 8:11).
5:7-9 The witness of the Spirit, together with Jesus' baptism and crucifixion, all three point to the fact that the Father has confirmed that Jesus was indeed his eternal Son.
5:10 Those who have faith know this, but unbelievers reject what God has clearly revealed through the witness of the Baptism, the cross and resurrection, and the work of the Spirit.
5:11 By God's own confirmation the eternal life that he offers is in and through his Son (John 3:16).
5:12 Which means that apart from the Son of God eternal life is impossible.
5:13 This is why John can assure those who believe in the Name (expressive of all of his character and power) of the Son of God that they have this eternal life.
5:14-15 This assurance gives us great boldness in prayer. We are not outsiders wondering if God will bother with us. As little children in a loving family we can be sure that we will receive all that we need (the only gifts that are not given are those that will harm us at this stage of our life).
5:16-17 The assurance of our status as children of God also gives us the right to pray for others. A mortal sin is not a question of how bad the person is, but of heart direction. No amount of prayer will help those who have already settled their choice of darkness and eternal death (John 3:19-20). But all other forms of wrongdoing can be forgiven, which is why we can pray for those who fall into every kind of sin which is obviously not a final choice of eternal death.
5:18-19 John again reminds us that those who have been born into the family of God do not choose to engage in deliberate sin (as in 3:6-10). The Son of God can protect his brothers and sisters and free us from the powers of evil that surround us. We may fail, but the Son keeps absorbing our sin in his body as the continuing atoning sacrifice for all people (2:1-2).
5:20 We also know that the Son of God has given us the power to understand the mind of God, and abide in his truth.
5:21 An idol localizes, caricatures, and reduces God to something we think we can manipulate. Which is why any idea, or rite, or image which is not the mind of God becomes an idol. And any kind of idol will take away the assurance that John has tried to give us. Idol priests are never satisfied; they always demand more. Their idols may seem impressive, but they can never give us the assurance of being totally loved as the very children of God.