Here's a practical way of considering this. Would you consider a person a Christian if he/she denies the deity of Jesus Christ? What if you believe the gift of tongues is still operable today, but your friend does not? Is that a reason to break fellowship? Or what about baptism? You think it's immersion but your Prebyterian friend believes sprinkling is the proper method. Can you still consider one another Christians?
Remember - the question isn't "Can both be right?" That's obvious - there is only one proper interpretation to any Bible passage. When two people disagree there are only two options: one is right and the other is wrong or they're both wrong. No, the question we're considering is this, "Which doctrines can you be wrong on and still be "safe?" Do you HAVE to get baptism right to be a Christian? Do you have to get the gifts right? Do you have to be right about Jesus?
I was reminded of an article written by Dr. Al Mohler that offered three helpful "categories" for doctrines and the consequences of not holding to them. He describes these as "three different levels of theological urgency, each corresponding to a set of issues and theological priorities found in current doctrinal debates."
Here are his suggested levels (emphasis mine):
First-level theological issues would include those doctrines most central and essential to the Christian faith. Included among these most crucial doctrines would be doctrines such as the Trinity, the full deity and humanity of Jesus Christ, justification by faith, and the authority of Scripture.You can read the entire article here. I trust this will help you make discerning decisions regarding our sacred Scripture and your fellowship with other believers.
These first-order doctrines represent the most fundamental truths of the Christian faith, and a denial of these doctrines represents nothing less than an eventual denial of Christianity itself.
The set of second-order doctrines is distinguished from the first-order set by the fact that believing Christians may disagree on the second-order issues, though this disagreement will create significant boundaries between believers. When Christians organize themselves into congregations and denominational forms, these boundaries become evident.
Second-order issues would include the meaning and mode of baptism. Baptists and Presbyterians, for example, fervently disagree over the most basic understanding of Christian baptism. The practice of infant baptism is inconceivable to the Baptist mind, while Presbyterians trace infant baptism to their most basic understanding of the covenant. Standing together on the first-order doctrines, Baptists and Presbyterians eagerly recognize each other as believing Christians, but recognize that disagreement on issues of this importance will prevent fellowship within the same congregation or denomination.
Christians across a vast denominational range can stand together on the first-order doctrines and recognize each other as authentic Christians, while understanding that the existence of second-order disagreements prevents the closeness of fellowship we would otherwise enjoy. A church either will recognize infant baptism, or it will not. That choice immediately creates a second-order conflict with those who take the other position by conviction.
Third-order issues are doctrines over which Christians may disagree and remain in close fellowship, even within local congregations. I would put most of the debates over eschatology, for example, in this category. Christians who affirm the bodily, historical, and victorious return of the Lord Jesus Christ may differ over timetable and sequence without rupturing the fellowship of the church. Christians may find themselves in disagreement over any number of issues related to the interpretation of difficult texts or the understanding of matters of common disagreement. Nevertheless, standing together on issues of more urgent importance, believers are able to accept one another without compromise when third-order issues are in question.
[This three-tiered classification] does not imply that Christians may take any biblical truth with less than full seriousness. We are charged to embrace and to teach the comprehensive truthfulness of the Christian faith as revealed in the Holy Scriptures. There are no insignificant doctrines revealed in the Bible, but there is an essential foundation of truth that undergirds the entire system of biblical truth.