None of this means that doctrinal differences do not matter at all or should be ignored. Areas of disagreement ought to be discussed. It is just that there are theological differences which do not merit the discontinuation of fellowship. There must be a balance between unity and separation. Some teachings of Scripture are clearer than others.
Doctrines that concern the Person and work of Jesus Christ, for example, are what we should consider essential in nature. The nature of sin is another example of an essential doctrine. These are uncompromisable tenets. Eschatology, ecclesiology, and modes of baptism are examples of nonessential doctrine. Certain elements may even belong in the realm of mystery.
The Apostle Paul uses meats as an illustration of how to interact with other believers on issues of secondary or tertiary importance (Romans 14:1-23). Examples of grey areas in our modern world would include whether or not one can drink wine, which college to attend, or go to a movie theater. These are matters of conscience which must be handled in a charitable fashion.
Paul spoke of matters that are "of utmost importance" (1 Corinthians 15:3). Thus, the gospel is to be the source of unity amongst all Christians. It is the power of God that brings salvation to everyone who believes (Romans 1:16).
Moreover, having perfect doctrine cannot be a requirement for salvation because that would be a work of righteousness. That is something which the Apostle Paul would argue against (Ephesians 2:8-9; Titus 3:5-7). A separatist and relativist approach to doctrine are both extremes that we should avoid.