Almost every denomination of Christianity rejects the idea that a person can know for certain, before they die, whether they will go to Heaven or Hell.
This is the logical outcome of what they believe a person must do to get to Heaven. Such believe that how a person behaves will ultimately determine whether they go to Heaven or Hell, regardless of the varying amounts of lip-service that they pay to believing in Salvation by faith or grace alone.
In such a situation, of course you can't know where you are going when you die. These groups see such an assertion as the height of arrogance and pride, as you are essentially saying that you know that you are good enough, and will continue until death to be good enough, to please God at the judgement. That is tremendously proud.
It should give such people pause, then, to learn that the Bible unambiguously teaches that someone can know for certain that they will go to Heaven, before they die, and regardless of whatever takes place between the present and their deaths.
Firstly, the Bible is replete with statements of living people affirming that they, and others, will go to Heaven when they die.
Job, in the Old Testament, said:
Job 19:25-26
25 For I know that my redeemer liveth, and that he shall stand at the latter day upon the earth:
26 And though after my skin worms destroy this body, yet in my flesh shall I see God:
King David said:
Psalm 23:6
6 Surely goodness and mercy shall follow me all the days of my life and I will dwell in the house of the Lord for ever.
John, writing to others, said:
1 John 5:13
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, and that ye may believe on the name of the Son of God.
Peter said, writing of other believers:
1 Peter 1:3-5
3 Blessed be the God and Father of our Lord Jesus Christ, which according to his abundant mercy hath begotten us again unto a lively hope by the resurrection of Jesus Christ from the dead,
4 To an inheritance incorruptible, and undefiled, and that fadeth not away, reserved in heaven for you,
5 Who are kept by the power of God through faith unto salvation ready to be revealed in the last time.
The Apostle Paul said:
2 Timothy 1:12
12 For the which cause I also suffer these things: nevertheless I am not ashamed: for I know whom I have believed, and am persuaded that he is able to keep that which I have committed unto him against that day.
And in the same book he said:
2 Timothy 4:18
18 And the Lord shall deliver me from every evil work, and will preserve me unto his heavenly kingdom: to whom be glory for ever and ever. Amen.
Paul, writing to others, said:
Romans 8:38-39
38 For I am persuaded, that neither death, nor life, nor angels, nor principalities, nor powers, nor things present, nor things to come,
39 Nor height, nor depth, nor any other creature, shall be able to separate us from the love of God, which is in Christ Jesus our Lord.
And Paul said yet again:
Philippians 1:23
23 For I am in a strait betwixt two, having a desire to depart, and to be with Christ; which is far better:
These men not only knew that they were going to Heaven, but often said the same of their audience or other believers, none of which would make any sense if no one could know whether they were going to Heaven or Hell until after they were dead.
Adding to these statements, remember how believers are always referred to as "the saints" (Romans 8:27, 12:13, 15:25, 16:15, Psalm 30:4, 31:23, Colossians 1:2, 1:4, 1:12, 1:26, etc., etc.)?
A "saint" is "one who is sanctified". And, if you understand the following verse, you will see that each of the references to "the saints" is referring to people who are being declared to be destined for Heaven:
Hebrews 10:14
14 For by one offering he hath perfected for ever them that are sanctified.
Since all who are sanctified are perfected "for ever", then every reference to a "saint, the saints, ye saints", etc., is referring to people who are perfected forever.
Therefore, as covered in the article Every Believer is a Saint, these are all instances of living people being declared to be destined for Heaven.
Highlighting one of the verses above leads to another important point:
1 John 5:13
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, and that ye may believe on the name of the Son of God.
Above, living people are told that they are to "know that ye have" - present tense - "Eternal Life". That means, by the definition of "eternal", that they will never perish in the Second Death (Revelation 20:14).
Eternal Life is spoken of as a present possession three other times in Scripture:
John 3:36
36 He that believeth on the Son hath everlasting life: and he that believeth not the Son shall not see life; but the wrath of God abideth on him.
John 6:47
47 Verily, verily, I say unto you, He that believeth on me hath everlasting life.
John 5:24
24 Verily, verily, I say unto you, He that heareth my word, and believeth on him that sent me, hath everlasting life, and shall not come into condemnation; but is passed from death unto life.
Notice especially, John 5:24. In this verse Jesus says that anyone who believes "is passed from death unto life". It's a completed operation, spoken of in the past tense, not a lifelong process.
All of the above also state that Eternal Life is obtained by faith. That's why it can be a present possession. If it required arduous struggle throughout one's entire life, then of course it couldn't be a present possession.
Works-trusting Christians therefore, propose two impossibilities in order to nullify these verses, which refute their self-righteous false religions, and they are as follows:
In response to the first point, no, Eternal Life cannot be lost, by basic definition of the word "eternal", and many Scriptural proofs, as covered in the article Top Ten Verses Proving Eternal Security.
To the second point, no, "belief" cannot be redefined to mean "obedience", as covered in the article You Do Not Have to Keep the Law to be Saved, because, in conjunction with the points discussed in that article, "faith" is explicitly separated from "works" by the Lord:
Romans 4:5
5 But to him that worketh not, but believeth on him that justifieth the ungodly, his faith is counted for righteousness.
Therefore, the Bible is clear in stating that Eternal Life is a present possession for all those that believe, meaning anyone who has put their faith in Jesus Christ to save them from Hell can know for certain that they will go to Heaven when they die.
In summary, the only way that someone could logically know that they will go to Heaven when they die is if the basis for that knowledge is their faith in Jesus Christ.
The fact that the Scripture makes it clear that you can know, presently, that you have Eternal Life, and gives many testimonies of other living people who knew the same thing, is proof that faith in Jesus Christ is something that happens in a moment in time, and can be known to have happened by those to whom it happened, while they are still alive.
If, in contrast, works were required to get to Heaven, this would be impossible to know, which yet another powerful argument against the self-righteous lie that how you behave determines whether you go to Heaven or Hell when you die.