Most true believers have witnesses to tell them about Jesus many times before they finally believe. Many times that transition from head knowledge, provided by either a person, TV or radio, to truly believing occurs when you personally open the Word and start asking questions. The Word and the Holy Spirit work together in your life to teach you those great truths of salvation and its only then that most people truly believe. It is not an easy thing for someone to let go of self sufficiency and trust in someone else.
Be patient with someone that knows all of the answers, but has had no life change, just point them to the Word. The good thing about quoting scripture is that they can't argue with your opinion, they need to wrestle with God. Maybe this person was even baptized and a Church member for years, but that doesn't mean they are saved. Send them to read through I John and the Holy Spirit will confirm their salvation if it is really there.
The stakes are high, be bold to ask someone if they truly know Jesus as Savior and Lord.
For His beautiful name,
Sent from my iPad