Scripture answers these questions:
Scripture Is Profitable
2 Timothy 3:16-17
All scripture is...
- Profitable for doctrine.
- For reproof and correction.
- For instruction in righteousness.
- That the man of God may be perfect, thoroughly furnished unto all good works.
2 Timothy 2:15
Study...
- To shew thyself approved unto God, a workman that needeth not to be ashamed.
- Rightly dividing the word of truth.
Discernment Is Given
Matthew 7:20
Ye shall...
- Know them by their fruits.
- Do men gather grapes of thorns, or figs of thistles? Even so every good tree bringeth forth good fruit; but a corrupt tree bringeth forth evil fruit.
- A good tree cannot bring forth evil fruit, neither can a corrupt tree bring forth good fruit. Every tree that bringeth not forth good fruit is hewn down, and cast into the fire.
1 John 4:1
Beloved, believe not every spirit, but try the spirits whether they are of God: because many false prophets are gone out into the world.
Either the doctrine is scripturally sound or it isn't. Possible reasons why doctrine isn't scripturally sound.
Satan
1 Peter 5:8
Be sober, be vigilant; because your adversary the devil, as a roaring lion, walketh about, seeking whom he may devour.
False Christs
Galatians 1:6-7
I marvel that ye are so soon removed from him that called you into the grace of Christ unto another gospel: Which is not another; but there be some that trouble you, and would pervert the gospel of Christ.
2 Thessalonians 2:8-10
And then shall that Wicked be revealed, whom the Lord shall consume with the spirit of his mouth, and shall destroy with the brightness of his coming: Even him, whose coming is after the working of Satan with all power and signs and lying wonders, And with all deceivableness of unrighteousness in them that perish; because they received not the love of the truth, that they might be saved.
Tradition of Men
Mark 7:8
For laying aside the commandment of God, ye hold the tradition of men, as the washing of pots and cups: and many other such like things ye do.
Colossians 2:8
Beware lest any man spoil you through philosophy and vain deceit, after the tradition of men, after the rudiments of the world, and not after Christ.
I'll answer this question with a question:
Q: What is the state of the conscience of the human(s) in question?
Character of God
Matthew 5:48
Be ye therefore perfect, even as your Father which is in heaven is perfect.
1 John 2:6
He that saith he abideth in him ought himself also so to walk, even as he walked.
Matthew 6:33
But seek ye first the kingdom of God, and his righteousness; and all these things shall be added unto you.
Romans 6:12-18
Let not sin therefore reign in your mortal body, that ye should obey it in the lusts thereof. Neither yield ye your members as instruments of unrighteousness unto sin: but yield yourselves unto God, as those that are alive from the dead, and your members as instruments of righteousness unto God. For sin shall not have dominion over you: for ye are not under the law, but under grace. What then? shall we sin, because we are not under the law, but under grace? God forbid. Know ye not, that to whom ye yield yourselves servants to obey, his servants ye are to whom ye obey; whether of sin unto death, or of obedience unto righteousness? But God be thanked, that ye were the servants of sin, but ye have obeyed from the heart that form of doctrine which was delivered you. Being then made free from sin, ye became the servants of righteousness.
Are men servants of righteousness or servants of sin?
Conclusion
All of these things are reasons why there are so many denominations, why some of them bear no fruit and why false doctrine can rise to global acceptance. Just because a doctrine is widely accepted doesn't mean it's scripturally sound. In fact, scripture would tend to point to that not being the case.
Matthew 7:13-14
Enter ye in at the strait gate: for wide is the gate, and broad is the way, that leadeth to destruction, and many there be which go in thereat: Because strait is the gate, and narrow is the way, which leadeth unto life, and few there be that find it.
Let's not forget that these things were prophesied to happen. Satan has crept into the body of Christ, in every denomination to some degree. Scripture is our only means of determining the truth—through prayerful supplication, through the Holy Spirit. If we are truly centered in our walk with Christ, doing as we are called to do, we will easily discern and reject false doctrine.
Ephesians 4:23-24
And be renewed in the spirit of your mind; And that ye put on the new man, which after God is created in righteousness and true holiness.
1 Corinthians 2:14
But the natural man receiveth not the things of the Spirit of God: for they are foolishness unto him: neither can he know them, because they are spiritually discerned.