Oh, @RobynH - I am so sorry that someone has disturbed you by saying that it is heretical to ask Jesus into your heart - or that it leads to false converts. I have heard this before - people saying that the Bible nowhere talks about asking Christ into your heart. Actually, Paul himself prayed for the Ephesians that Christ may dwell in your hearts by faith in Ephesians 3:17.
Sometimes I think people get a bit carried away by insisting too particularly about how one phrases their trust in Christ. There are many ways you can word the concept, but the wording itself isn’t really the issue. Trusting Christ’s death to pay the penalty for your sins, trusting His resurrection to raise you to new life, that’s really all salvation is.
Now, your specific question was how to know that you’re really saved - what does genuine salvation look like.
Well, the little letter of I John was specifically written to answer that very question. I John 5:13 says, These things have I written unto you that believe on the name of the Son of God that ye may know that ye have eternal life…
As you go through the letter, you’ll keep seeing phrases like hereby we know that we know him and hereby know we that we are in him and hereby we know that he abideth in us and so on.
So what are these things that he keeps saying we know we’re saved by?
Well, there are three tests that he keeps repeating throughout the book over and over. They are:
True Christians walk in the light
True Christians love the brethren
True Christians believe the truth
When he says that true Christians walk in the light (and that’s phrased in various ways in the book), he means that their lifestyle is moving toward God (He is the Light - 1:5). Do you genuinely desire to please and honor God by your life? Do you want to obey His word? Are you truly grieved when you sin. If so, then you pass this test. But remember, we’re talking about direction, not perfection. If you’re moving toward the light, you still may stumble - every child learning to walk does. But you’re stumbling toward the light!
When he says that true Christians love the brethren, that doesn’t mean that our Christian brethren won’t ever get on our nerves, or us on theirs. We’re all works in progress, and learning to love as God does is the hardest thing we’ll ever do. It’ll take a lifetime, and we’ll never get it down perfectly. But can you truly say that Christians who love Christ are the kind of people you most want to be with? Are you more comfortable with godly Christians than you are with worldly minded people? If so, then you pass the love test.
And when he says that true Christians believe the truth, he’s talking about the truth concerning Who Christ is and what He did to save us. Christians may differ on many peripheral things, so obviously not everything we believe is true. And Christians may change their minds on things like baptism or predestination or charismatic gifts or eternal security, etc.
But a true Christian will never really change his mind about Jesus being the virgin born, sinless Son of God Who died on the cross and rose again for our salvation - or that faith in His gospel is the only condition for a repentant sinner to be saved. If you can truly say that you believe these essential things about Who Jesus is and what He did to save us, then you’ve passed the belief test.
And as a footnote, I’ll just add that salvation is really an all or nothing proposition. Either a person really is a Christian and he passes all the tests, or he’s really not a Christian and he passes none of them. There’s no such thing as being partly Christian and passing one or two. So if you pass any of these tests, it naturally follows that you pass them all.
That verse I mentioned back at the start - I John 5:13 - these things have I written unto you that believe on the name of the Son of God that ye may know that ye have eternal life - it ends by saying, and that ye may believe on the name of the Son of God.
In other words, if someone sees that they really don’t pass these tests, then John’s secondary purpose for writing the letter is so that they truly will believe on the name of the Son of God and then they’ll begin passing them after all.
I truly hope that these thoughts will bring you peace.