Are you convinced they know Christ as Savior?

Recently a professor commented that there is no way we can know whether anyone knows God in their heart unto salvation. "Only the Father knows those who belong to Him," he said. I thought, "Really?" Questions popped up immediately. At that comment I interrupted and asked him, "Are you telling me there is no way I can know that my wife knows the Lord?" Does not Scripture tells us to not be unequally yoked with an unbeliever. As much as I love my professor, his comments, I am convinced, are wrong. Has not God given us the Holy Spirit and common sense to perceive those who belong to Him? Does not are spirit bear witness with those who belong to the family of God? Wow! Can we not see the love for God, the humility, the passion for God's glory in an individual and say to ourselves, "That is a person of God." Sure "Christians" everywhere are working out their own salvation, and many claim to do things in Christ's name that are phonies, but is not there a place where you and I find comfort in knowing that there are those we know who love the Lord when we fellowship with them?
I know that I know that I know that my lovely wife, Kathy, knows the Lord. Her character displays the things in Scripture that tell me she is a follower of Christ. There is no doubt in my mind or my heart.
We can especially tell those who belong to the family of God when trails come. Look...all I am saying is that there are indicators along the way. There is much more I would have to say on this comment but I am restraining myself for the sake of my readers. There is tremendous comfort when I dwell in fellowship with other believers of Christ whether I know them or not. It is the coming together of those who love the Lord where the Holy Spirit dwells; Scripture tells us that. Also in 2 Timothy 2:5 Paul writes to Timothy and says, "I am reminded of your sincere faith, a faith that dwelt first in your grandmother Lois and your mother Eunice and now, I am sure, dwells in you as well. How could Paul say, "I am sure..."? Well, I know how he could say it. It's called overwhelming evidence that their character lines up with God's Word of holy living.
It breaks my heart for anyone to think there is no one we can trust in fellowship. I consider it lonely and tragic. Peace out ~