Weekly Sermon Insights: What We Know for Certain (1 John 5:6-21)
Assurance matters!
August 16, 2026
Tim Bower
Message Notes
Study Notes: 1 John 5:6–21 — What We Know for Certain
Passage Focus
Primary text: 1 John 5:6–21
Theme: What do we know for certain? Certainty and assurance in the Christian life.
The word "know" appears 39 times throughout 1 John (8 times in chapter 5 alone) — a major theme of the entire epistle.
Main Idea
John writes to give believers confident assurance of their faith. He identifies specific truths that Christians can know for certain, supported by divine testimony and evidence.
Textual Note: 1 John 5:7 (The Comma Johanneum)
The teacher noted that if you are reading from the KJV or NKJV, verse 7 includes an extra phrase about the Trinity (the "heavenly witnesses" passage) that does not appear in the ESV or most modern translations. This longer wording is absent from the earliest Greek manuscripts and was likely added by a scribe in later Latin tradition. It neither adds to nor detracts from orthodox doctrine, but it is not part of the original Greek text. The teacher was reading from the ESV.
The Five Certainties
1. We Know That Jesus Is God (vv. 6–10)
This is a matter of Christology — the question of who Jesus Christ is.
Peter declared it in Matthew 16:16: "You are the Christ, the Son of the living God."
The teacher referenced the classic "liar, lunatic, or Lord" argument (commonly attributed to C.S. Lewis, though the teacher heard it from R.C. Sproul): given what Jesus said and did, He must be Lord.
Three Witnesses to Jesus as the Son of God:
Witness | Meaning | Supporting Text |
The Spirit | The Holy Spirit, who testifies within believers' hearts | John 15:26 — "The Spirit of truth... will bear witness about me" |
The Water | Jesus's baptism in the Jordan, where the Father's voice declared Him Son | Matthew 3:17 — "This is my beloved Son..." |
The Blood | Jesus's crucifixion, accompanied by supernatural signs and testimony | Matthew 27:51–54 — the centurion: "Truly this is the Son of God" |
The teacher preferred the interpretation that "water and blood" represent the bookends of Jesus's ministry (baptism and crucifixion), rather than the alternative theory that it refers to the blood and water that flowed from Jesus's pierced side at the cross (John 19:34).
This language may also have been intended to counter early false teaching (associated with Cerinthus) that denied the virgin birth, claimed Jesus was merely the natural son of Mary and Joseph, and taught that divine power came upon Him at baptism but left before the crucifixion.
2. We Know That Believers Have Eternal Life (vv. 11–13)
Verse 11: "God gave us eternal life, and this life is in His Son."
Verse 13: "I write these things to you who believe... that you may know that you have eternal life."
Eternal life is a gift from God, not earned by works.
Ephesians 2:8–9 — "By grace you have been saved through faith... not of works."
John 10:27–28 — "I give them eternal life, and they will never perish."
2 Timothy 1:12 — "I know whom I have believed, and I am persuaded that He is able to keep what I have committed to Him."
The purpose of John's writing is assurance — that believers can know with certainty they possess eternal life.
3. We Know That God Answers Prayer (vv. 14–15)
Verse 14: "If we ask anything according to His will, He hears us."
Verse 15: "If we know that He hears us... we know that we have the requests that we have asked of Him."
Conditions and caveats:
Prayer must be according to God's will — it is not a blank check.
God knows more than we do; sometimes the answer is no or not yet.
We will not change God's mind or explain things to Him — He already knows His will.
Why pray if God already knows?
God commands us to pray and desires communication with us.
The act of praying is beneficial to the believer, even when the answer is no.
The teacher cited Hudson Taylor (missionary to China) and George Müller (ran an orphanage in England) as examples of lives marked by remarkable answers to prayer.
4. We Know That Christians Do Not Practice Sin (vv. 16–19)
Verse 18: "Everyone who has been born of God does not keep on sinning."
This repeats the teaching from 1 John 3:9 — a lifestyle of continued, habitual sin is incompatible with the Christian life.
We all still sin (Romans 3:23), but we are not to continue in it.
How can believers avoid continuing in sin?
Jesus protects the believer (v. 18) — "He who was born of God protects him, and the evil one does not touch him."
Jesus prays for us — Luke 22:31–32: "Satan demanded to have you... but I have prayed for you that your faith may not fail."
The Word of God — 1 John 2:14: "The word of God abides in you, and you have overcome the evil one." Also Ephesians 6:17: "The sword of the Spirit, which is the word of God."
The "Sin That Leads to Death" (v. 16):This passage raises a difficult question. The teacher noted three possible interpretations:
Interpretation | Explanation | Assessment |
Spiritual death for believers | Some who reject eternal security teach that a believer's sin can cause loss of salvation | The teacher considered this wrong |
Physical death (capital punishment) | God's judgment on believers whose actions threaten the body of Christ (OT examples below) | Possible, though its ongoing applicability is uncertain |
Spiritual death for nonbelievers | Refers to those who flatly reject the gospel | Possible, though it seems like John says a lot if this is all he meant |
Scriptural examples of physical death as divine judgment:
Nadab and Abihu — Leviticus 10 (offered unauthorized fire)
Korah and his followers — Numbers 16 (rebelled against Moses)
Achan — Joshua 7 (disobeyed God's command at Jericho)
Uzzah — 2 Samuel 6 (touched the ark)
Ananias and Sapphira — Acts 5 (lied to God about their offering)
Believers in Corinth — 1 Corinthians 11:30 (died because of misconduct at the Lord's Supper)
The teacher concluded that the exact meaning is uncertain and "probably not something worth spending a lot of time worrying about."
5. We Know That the Christian Life Is Founded on Truth (v. 20)
Verse 20: "The Son of God has come and has given us understanding, so that we may know Him who is true."
This speaks to the benefits of being in the family of God — understanding, truth, and a relationship with the true God.
What people are really seeking:
Peace and relief from guilt
Meaning and purpose
Hope of eternal life
The power of love and righteousness
Assurance that their beliefs are founded on truth
The teacher reflected: when people are called "seekers," what they seek is described in verse 20 — the benefits only God can give. (Referenced Genesis 3: God wasn't hiding in the garden — Adam and Eve were.)
Verse 21 — "Keep yourselves from idols":
Not an afterthought, but a deliberate contrast to verse 20.
The true God offers understanding, life, and truth; idols offer nothing.
In Ephesus (where many of John's readers likely lived), the manufacture and sale of idols was a major industry.
Modern idols — whether financial, relational, or otherwise — can be just as damaging as ancient ones.
Summary: The Five Certainties
# | Certainty | Key Verse | Supporting Texts |
1 | Jesus is the Son of God | vv. 6–10 | Matthew 16:16; John 15:26; Matthew 3:17; Matthew 27:51–54 |
2 | Believers have eternal life | vv. 11–13 | Ephesians 2:8–9; John 10:27–28; 2 Timothy 1:12 |
3 | God answers prayer | vv. 14–15 | (conditions: according to His will) |
4 | Christians do not practice sin | vv. 16–19 | 1 John 3:9; Romans 3:23; Luke 22:31–32; Ephesians 6:17 |
5 | The Christian life is founded on truth | vv. 20–21 | Genesis 3 (God is not hiding) |
Application Points
Assurance matters: John wrote so that believers would know they have eternal life — not just hope or suspect it.
God's testimony is greater than human testimony: The Spirit, water, and blood all confirm that Jesus is the Son of God.
Prayer is a relationship, not a transaction: We pray because God commands it and because it draws us closer to Him — even when the answer is no or not yet.
Sin should not be our habit: While we still stumble, habitual sin is incompatible with new life in Christ. We have Jesus's intercession, the Word, and the Spirit to help us.
Truth is the foundation: The Christian faith is not based on myths or idols but on the true God who has revealed Himself through His Son.
Examine your idols: What substitutes for God in your life may be just as destructive as the literal idols John's first readers faced.
Discussion Questions
Why do you think the theme of "knowing" is so prominent throughout 1 John? What difference does assurance make in the Christian life?
How do the three witnesses — the Spirit, the water, and the blood — work together to confirm that Jesus is the Son of God?
What does it mean to pray "according to His will"? How should we respond when the answer is no?
If believers don't lose salvation, what does "sin that leads to death" (v. 16) likely mean?
What does it look like practically to "keep on sinning" versus occasionally stumbling? How do we distinguish the two?
What "idols" — modern substitutes for God — are most tempting in our culture today?
How does verse 20 challenge the idea that truth is relative or unknowable?
Reference Notes
Cerinthian teaching: Cerinthus is associated with an early Christological error that separated the divine Christ from the human Jesus. Labeling it "Gnostic" is somewhat debated among scholars, but it represents an early false teaching that John's language may counter.
Closing Prayer Emphasis
• Five certainties:
1. Jesus is God.
2. We have eternal life.
3. God hears and answers prayer.
4. We are delivered from the power of habitual sin.
5. We rest in the One who is true.
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