The Bible says we should have inner assurance from the Holy Spirit:

"Hereby know we that we dwell in him, and he in us, because he hath given us of his Spirit"  "The Spirit itself beareth witness with our spirit, that we are the children of God"  “My sheep hear my voice, and I know them, and they follow me:”  "And he that keepeth his commandments dwelleth in him, and he in him. And hereby we know that he abideth in us, by the Spirit which he hath given us." “He that believeth on the Son of God hath the witness in himself:” “And the work of righteousness shall be peace; and the effect of righteousness quietness and assurance for ever.”  “Examine yourselves, whether ye be in the faith; prove your own selves. Know ye not your own selves, how that Jesus Christ is in you, except ye be reprobates?”

Have I experienced the Holy Spirit? (NOT in the charismatic sense)  Or do I just know ABOUT Him and believe that I have Him inside of me because I can point to a scripture verse that says that He should be there?  Intellectual (pretend) 'salvation'; versus Spirit wrought illumination.  Mental assent to facts; versus Spirit wrought illumination.  The difference is Life and death.

The only thing that ultimately matters that we each must ask ourselves is: Am I a reprobate?
Do I "know" (the word “know” means an intimate personal knowledge, the same "know" as used for marriage)?  Assurance comes from inside - from the Holy Spirit.  I know that He is there because He talks with me and teaches me, and manifests Himself to me, and helps me to yield the fruits of the Spirit as I walk the "narrow way" in strict obedience; not because I can point to a Bible verse that says that He should be there.

The hymn says: "And He walks with me and He talks with me and He tells me I am His own".  This is not pretend.  Or beautiful symbolism or poetry:  "My sheep hear my voice".

“Now if any man have not the Spirit of Christ, he is none of his.”

If someone doesn't know that they have the Holy Spirit on a level that "passeth knowledge" (not simply from a mental/intellectual pointing to a Bible verse) than He is not born again, not a believer, and is not abiding in eternal life.
Don't delude yourself. 

The gate is "strait" and "few there be who find it".

"Strive to enter in at the strait gate".
from William Dyer, 1632-1696

The Word of God is the Christian's rule—and the Spirit of God is the Christian's guide.

"To the law and to the testimony: if they speak not according to this word, it is because there is no light in them." Isaiah 8:20. "We have also a more sure word of prophecy; whereunto ye do well that ye take heed, as unto a light that shineth in a dark place, until the day dawn, and the day star arise in your hearts" 2 Peter 1:19. "All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness" 2 Timothy 3:16. "Howbeit when he, the Spirit of truth, is come, he will guide you into all truth" John 16:13.

Most people walk by false rules:

1. Some walk by popular opinions.

2. Some walk by worldly customs.

3. Some walk by providence.

4. Some walk by conscience.

5. Some walk by their own reason.

6. Some walk by other men's examples.

7. Some walk by their own lusts.

But, oh! my dear friends, let me beseech you to walk by none of these false rules—but keep close to the Word and Spirit of God.

The Scripture is a rule outside of us, to show as where we must go; the Spirit is a guide inside of us, to enable us to walk according to the direction of that Word. The Word of God is a compass, by which we must direct our course; the Spirit is the great pilot, who steers us in this course. We have no eyes to see the Word—until the Spirit enlightens them. We have no ears to hear the Word—until the Spirit opens them. We have no hearts to obey the Word—until the Spirit bows and inclines them.

By the Word of God—we know the mind of the Spirit of God. And by the efficacy of the Spirit—we feel the power of the Word. The Word of God shows us the way; and the Spirit of God leads us in that way which the Word points out. The Spirit of God is able to expound the Word of God, and to make it plain to our understanding. The Holy Spirit is the Christian's interpreter; he gives the Scriptures, and he alone can reveal unto us the sense and meaning of the Scriptures. The Word is God's counsel, to reveal the path in which we are to walk; the Spirit is God's Counselor—who teaches us to walk in that path. The Word is a looking-glass, which shows us our duty. If God had not put his Spirit into our hearts, as well as his Word into our heads—we would never have arrived at the fair haven of peace.

The Scriptures reveal the very heart of God. God Almighty has, in the sacred Scriptures, as it were, manifested himself, unfolded all his counsel to the creatures, as far as is necessary to be known for their direction and guidance to everlasting life."