Quoting the Lord Jesus, the Apostle John wrote, »Behold, I stand at the door (of your heart) and knock; if anyone hears My voice and opens the door, I will come in to him.« (Revelation 3:20) Receiving Christ involves turning to God from self (the Bible calls this ‘repentance’), and trusting Christ to come into our lives to forgive all our sins (past, present and even future) and to make us the kind of people He wants us to be. However, just to agree intellectually that Jesus Christ is the Son of God and that He died on the cross for our sins is not enough. Nor is it enough to have an emotional experience. We receive Christ by faith as an act of the will.
If you have sincerely asked Jesus to forgive your sins and come into your life, you have His promise in Revelation 3:20 that He will come in and be your friend so you can know Him personally. Would He mislead you? You have it on His authority, the trustworthiness of God Himself, and His Word that God has answered your prayer.
The Bible promises eternal life to all who receive Christ. Again, the Apostle John wrote, »And the witness is this, that God has given us eternal life, and this life is in His Son. He who has the Son has the life; he who does not have the Son of God does not have the life. These things I have written to you who believe in the name of the Son of God, in order that you may know that you have eternal life.« (1 John 5:11-13)
Thank God often that Christ is in your life. Christ says in Hebrews 13:5, »I will never leave you or forsake you.« In the original Koinonia Greek language, that verse is more accurately translated, »I will never, no, not ever leave you or forsake you.« It is a triple, emphatic negative. You can know based on His promises that Christ lives in you and that you have eternal life, from the very moment you invite Him in. He will not deceive you. He is totally, wonderfully good and trustworthy!
A key to knowing you can have assurance of salvation is your obedience (1 John 2:3,4: »And by this … « Are you willing to submit to Christ’s Lordship in your life, and change in areas that God points out in His word and through His Spirit that are wrong? Are you willing to obey what God says regardless of your fears or the consequences? Moreover, the Apostle John wrote that the key ingredient to all of this of that our motivation should be love of God. (1 John 5:2,3)
The summary question remains, »Will you trust Him to save you when He promised He would if you asked sincerely and choose to follow Him in obedience?«