Pastor Bill responds (pt. 1):
The most masterful statement of assurance of salvation is found in the Westminster Confession of Faith, chapter 18, “Of Assurance of Grace and Salvation”. I urge you to study that with the Scripture proof texts. You will find that study richly rewarding.
That’s the easy way to answer your question - or at least to direct you to a very full answer!
But a simple answer to your question isn’t easy!
Frankly, more professed Christians should struggle with this issue as you do. Whether or not our sins are truly forgiven and whether or not we are truly Christians are the most important issues we face in this life. One of the scariest truths in the whole Bible is given in Matthew 7:21-23:
Not everyone who says to me, ‘Lord, Lord,’ will enter the kingdom of heaven, but the one who does the will of my Father who is in heaven. On that day many will say to me, ‘Lord, Lord, did we not prophesy in your name, and cast out demons in your name, and do many mighty works in your name?’ And then will I declare to them, ‘I never knew you; depart from me, you workers of lawlessness.’
“That day” is the day Judgment after Christ returns. All of us will stand before Jesus as the Judge on that day (see Acts 17:31). That includes professed Christians (those who called Jesus ‘Lord’). Many of these will be those who did “many mighty works” in Jesus Name. But (and this is what is very scary), Jesus will say to many of those, “I never knew you. Depart from me.”
We could say that the most important issue is not “Do you know Jesus?”, but “Does Jesus know you?” - Has Jesus given you specific evidences of His love for YOU?
The big evidence that we are loved and saved by God through Jesus Christ (according to this passage) is that we not only call Jesus Lord, but we obey Him. “If you love me, keep my commandments” (John 14:15, 21; 15:10, cf. I John 3:24). When the Lord saves us, He gives us a “new heart” (Ezekiel 36:26), and that “new heart” makes us want to obey God.
So, the answer to your question begins here: A true Christian wants to obey the Lord fully and from the heart. Do you?