Doctrine is a noun, another word for "teaching."
"Whom shall he teach knowledge? and whom shall he make to understand DOCTRINE? them that are wearned from the milk, and drawn from the breasts. For precept must be upon precept, precept upon precept/ line upon line, line upon line/ here a little, and there a little: For with stammering lips and another tongue will he speak to this people. To whom he said, This is the rest wherewith ye may cause the weary to rest; and this is the refreshing: yet they would not hear." Isa 28:9-12
The first thing Ac 2:42 says of the early Christians is that "...they continued stedfastly in the apostles' doctrine..."
Some churches and Christians want to stay away from doctrine, thinking that it is controversial and divides Christians, bringing disharmony. Without doctrine, we don't have God's teaching. The greatest teacher of all time was Jesus Christ. When the high priest questioned Jesus, Jn 18:19 says he asked Him about "his disciples, and of His doctrine."
Not only is there good doctrine, but there is also the opposite. Eph 4:14 says "That we henceforth be no more children, tossed to and fro, and carried about with every wind of doctrine, by the sleight of men and cunning craftiness, whereby they lie in wait to deceive;" 2Ti 4:3 tells us "For the time will come when they will not endure sound doctrine; but after their own lusts shall they heap to themselves teachers, having itching ears; (highly desirous to hear bad doctrine.)
Some don't believe in certain doctrines, while some just disagree on the interpretation of certain doctrines, or the application of certain doctrines.
Why do people interpret passages, verses, words differently?
Different definitions give different meanings and understanding.
Some have been taugh differently. Some feel differently. Some "want" to believe different than what the Bible teaches. Some want the Bible to agree with how they feel, rather than changing to agree with what the Bible says. Some don't understand the Bible correctly, or see it in its proper context. 2Ti 2:15 would have us "rightly divide" the Word, or understand it in its full context, knowing what time period a passage is for, what people it is for, and what the subject is that really is being addressed, comparing scripture with scripture. Some have been in error when they have thought the subject was "how to be saved" when it was really "how to live after one is saved."
Mormons are notorious for having different definitions than what most Christians have. Therefore they can talk to people that are unfamiliar with what Mormons really believe (using words people are familiar with like "church" and "Jesus") and lull them into becoming a part of the Mormon church.
How a person chooses a church to become a part of should be based more on the doctrine that church follows than on where the building is located, what the building looks like, how friendly the people are, how good the music sounds, the age-socio-economic-ethnic make-up of the congregation, or how interesting the preacher's sermons are. A church doesn't necessarily have to hold to every minor doctrine or belief that you hold to, but it should hold to most if not all of the major doctrines that you hold to, and hopefully these are the ones the Bible really teaches.
"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." Col 2:8
"For we are not as may, which corrupt the word of God:..." 2Co 2:17
"...not walking in craftiness, nor handling the word of God deceitfully;..." 2Co 4:2
"Be not carried about with divers and strange doctrines." Heb 13:9
Paul would write to Pas. Timothy in 1Ti 4:13 imploring him "Tiill I come, give attendance to reading, to exhortation, to doctrine."
In 2Timothy, Paul writing his last words of scriture before his approaching death would tell him in 3:16 "All scripture is given by inspiration of God, and is profitable for doctrine,...That the man of God may be perfect, throughly furnished unto all good works." In the final chapter of that book some of Paul's last words to Timothy were these: "Preach the word; be instant in season, out of season; reprove, rebuke, exhort with all longsuffering and doctrine. For the time will come when they will not endure sound doctrine;"
So we see from all of this how important doctrine, and the proper teaching of sound doctrine is to God. We can not just ignore it for the presumed sake of everyone then being able to get along.