11-12 And this is the testimony - that God gave us eternal life, and this life is in his Son!  Whoever has the Son has life; whoever does not have the Son of God does not have life. 13 I write these things to you who believe in the name of the Son of God that you may know that you have eternal life. 

14-15 And this is the confidence that we have towards him, that if we ask anything according to his will he hears us.  And if we know that he hears us in whatever we ask, we know that we have the requests that we have asked of him. 16 If anyone sees his brother committing a sin not leading to death, he shall ask, and God will give him life - to those who commit sins that do not lead to death. There is sin that leads to death; I do not say that one should pray for that. 17 All wrongdoing is sin, but there is sin that does not lead to death. 1 John 5:11-17 (English Standard Version)

What was a big reason why the apostle John wrote this letter? (vs 13)

He wanted those who'd put their faith and hope in Jesus Christ to know with certainty that they were indeed saved. He was affirming one of the most well known verses in the Bible which he'd written in his gospel saying: “God so loved the world that He gave His only begotten Son, that whoever believes in Him should not perish, but have eternal life.” (John 3:16) Christians don't just hope to get eternal life when they die – they possess eternal life already. What should this confidence lead to? (vs 14-15)

Christians can be confident that the invisible God whom Jesus revealed WILL hear their prayers. When His disciples were deeply troubled that Jesus was returning to His Father, Jesus comforted them by saying: “Truly, truly, I say to you, whatever you ask of the Father in my name, He will give it to you. Until now you have asked nothing in my name. Ask, and you will receive, that your joy may be full.” (John 16:23-24) This wasn't a 'blank cheque' to encourage us to ask God for worldly things. What did John have in mind when he encouraged Christians to pray with confidence? (vs 16)

Christians are to pray for one another to win the battle against sins that we so easily fall into. That’s especially true if we see a fellow Christian falling into sins that will cause them to drift from Christ. We don't know if John had in mind words Jesus spoke when people said His miracles were done through the power of Satan. Jesus said to them: “I tell you, every sin and blasphemy can be forgiven - except blasphemy against the Holy Spirit, which will never be forgiven. Anyone who speaks against the Son of Man can be forgiven, but anyone who speaks against the Holy Spirit will never be forgiven, either in this world or in the world to come.” (Matthew 12:31-32)

If some people in John's day who claimed to be Christians, but denied that Jesus was God's begotten Son and that He came in the flesh to save sinners, they were essentially denying and rejecting the gospel. Like those who made the Holy Spirit out to be a deceiver, such people were shutting the door to the truth that could save them. They were a lost cause. But John isn't saying that a believer who, for example, fell into serious sexual sin, or even denied knowing Jesus in a moment of panic (as Peter did when Jesus was arrested), can't be restored to an obedient walk with the Saviour. God's grace is amazing.

John was also not saying that, therefore, doing wrong things doesn't matter. See vs 17. The point John makes is that prayer is a big part of Christians overcoming sin. Not only sin in our own lives, but sin in the lives of others. When the Lord taught the disciples to pray, He said: “Forgive us our sins.” We are to pray for others too! And James (the Lord's brother) wrote: “Confess your sins to one another - and pray for one another that you may be healed. The prayer of a righteous person has great power as it is working.” (James 5:16)