17 Now the crowd that was with Him when He called Lazarus from the tomb and raised him from the dead bore testimony to this.
18 The crowd, also met with Him, because they had heard He had done this miraculous sign.
There are a couple of things for us to note from verse 17.
1 John again states that Jesus raised Lazarus from the dead. In stating this he again affirms the resurrection of the dead. This is at the core of our faith. Christianity is primarily based on the fact that God raised Jesus from the dead, and that all who believe in Him will also be raised from the dead. Paul stated: And if Christ has not been raised, then your faith is useless, and you are still under condemnation for your sins – 1 Corinthians 15.17 (NLT).
It is just possible that Lazarus was still alive when John wrote his gospel. It would have been a timely reminder to his readers that amongst them was one who had died, but was now alive. He was living proof of the mighty power of Jesus to conquer death.
On the other hand if Lazarus had already died by the time of writing, then it was good for people to look back to him whom some of them most likely knew. To look back and know that Lazarus had experienced the mighty power of Jesus to bring him back from death and give him many more years of life.
Lazarus was the living proof of the resurrection power of Jesus.