For by one offering he hath perfected for ever them that are sanctified. Whereof the Holy Ghost also is a witness to us: for after that he had said before, This is the covenant that I will make with them after those days, saith the Lord, I will put my laws into their hearts, and in their minds will I write them; And their sins and iniquities will I remember no more. (Heb 10:14-17)
The most shallow, baseless, and unscriptural means of assurance is often given to those who have been led through a prayer to reinforce what they just did. This usually sounds something akin to “whosoever believeth hath eternal life. What did you just do? Believe? Then according to 1 Jn 5:13 you know have eternal life”. This circular reasoning is entirely based on the actions of the “believer” to ensure them of their standing with God. This is something like holding your own hand while walking in the dark to keep from falling.
Scripture states in Hebrews 10:15, as well as Romans 8 that the Spirit of God is a witness to us of the work of God in our hearts, assuring us of our position in Christ. This witness is not some mystical feeling, but is actual fruit, made manifest as we are changed into the image of Christ. The fruit of the Spirit is not a laundry list of things to be added by the believer into his life, but is the very fruit OF THE SPIRIT. If you have the Spirit you will bear His fruit.
1 John 5:13, often quoted out of context, is a reference to the “these things” of 1 John. “These things” are written to give assurance that one knows they do indeed have eternal life. The entire epistle is a continual contrast of those who love God, and those who love the world. Those who love the brethren, and those who do not. Those who walk in light, and those who walk in darkness. In other words, EVIDENCE which can be examined to truly determine ones position with God.
God does not leave us to the resource of our own faith to know that we are in favor with Him. Again, this is like holding your own hand to keep from falling in the dark. His Spirit bears witness with our spirit. This witness is according to the manifestation of the sons of God as written in the word of God. Which gives us the ability to “examine ourselves, whether we be in the faith”.