LittleLion said:
How do you know you are sincere?
How can you be sure that you are not merely pretending to be sincere (even before yourself)? How do you know you are not merely displaying some wishful thinking of how you would like to be, but are not?
How do you know when you are telling the truth about yourself (like in prayer)?
Those are just about the best questions I have ever read on a Christian forum---and I've been on more than a dozen, for 3 years or more.
The fact is, we generally do not know, for we can not know apart from God specifically, supernaturally revealing it to us.
If I might take liberty by paraphrasing and amplifying Jeremiah 17:3: "The spiritual heart of a person is desperately wicked, and more than any other facet of it, it is deceitful to our own understanding of what evils live within its very self-protecting walls.
The Apostle Paul, the best example of the Christian life we have---apart from Christ himself of course---declared that he does not even judge his own self, that only God is able to do that. But since elsewhere we are commanded to judge ourselves, then by combining these two Truths, we can know that we must always be in the process of seeking God's judgment of us and our sicerity or lack thereof.
There's only one way (unless your crammed into a Turkish prison with numerous others and no time to yourself), and that is to get away by yourself each day, for whatever length of time you feel led (an hour is a good start), seeking the Heavenly Father, in Jesus' name, to reveal Himself and His assessment of you, to you. It may take several weeks or months of this at first, but I've been a believer for decades and know of no other way that works (even though many others will most likely disagree).
Similarly,
How do you know that you truly believe in Christ?
How do you know that you truly believe in Christ, and are not merely deluding yourself with wishful thinking?
God is very gracious, in that He doesn't make us rely on just one "witness" of His reality in our life, but He gives us several, that, when combined, will "assure our hearts before Him."
When we are born-again, for example, He gives us "His Spirit bearing witness with our spirit, that we are the children of God." (However, many who once genuinely experienced that, may presently be living off just the memory of it, and is yet one more reason we need several "witnesses.")
His written Word gives us assurances. See such as 2 John 2:3-5 (which takes some time to reach the state of, however, many fool themselves into believing they are in the process, when in truth they have long ago hardened their heart against God's attempts---again why it is not, by itself, enough).
God makes available to the born-again Christian, the instantly-given fullness of His Love whereby someone will find the immediately Love every person who was ever born, and all equally, and to the same degree that Christ Jesus Loved and died for us. So this is an indicator we are, or still are, in the Way of God---although someone can also harden their heart even after that, and again be living off just the memory of what once actually was.
Etc.
The Christian life can be summed up as one whereby we learn the moment-by-moment Voice of the (S)spirit, and then obey it. This will require receiving acts of Grace from God, one after the other (like the New Birth and like the fullness of Love), until most or all the evils of our heart are removed (because the drown out God's Voice), and until those evils are replaced with all the fullnesses of Christ (Fruits of the Spirit and Wisdom), or until we die.
But if along the way we harden our heart to what God is attemppting to do in our life, and rest on our laurels, we will lose our intimate relationship and be in doubt---just as it was meant to be; rightly so.
God bless, brother jim
"Today, if you will hear His Voice, harden not your hearts. . . ."
(But bearing our head in the sand so that we cannot hear, doesn't count.)