The divine elephant?
You may have heard the old analogy for religious variety - the parable of the blind men and the elephant. Humans are described as blind men search for religious truth. The divine is an elephant, and the differing religious views are the result of feeling different parts of the elephant without the ability to perceive the whole: the one who feels the tail perceives God as a snake, the one who feels the elephant's leg perceives God as a tree trunk, and so on.
The illustration is useful in that our blindness well models our epistemological ignorance: how does one really fully know and describe God? However, it also has limits. It seems to suggest that all religious knowledge is empirical and ignores the role of revelation, i.e. the idea that God is able and maybe even willing to reveal information about Godself that could not be inferred or reasoned to. It also sees the distinctive ideas in different religions as optional extras, things to be cast aside in favour of the a priori theory of the elephant. Neither of these is logically necessary.
The divine elephant is a universalist idea, that all religions say essentially the same thing. The opposite view is an exclusivist one, where only one religion contains "the truth". For example, Jesus' "I am the way, the truth and the life, no one comes to the Father by through me" would seem to suggest this - and exclucivism doesn't appear to be uniquely Christian. This is somewhat modified it seems to me by texts like Acts 17, where Paul at least could acknowledge the religiousity of the Athenians points towards God - so religious truth can be found in echo or shadow in some thinking without being clear of salvific.
One vista, many windows
Given I'm a Christian, I obviously lean towards Christianity containing the largest and most complete deposit of truth about divine revelation - nicely captured in the first chapter of Hebrews
God, after He spoke long ago to the fathers in the prophets in many portions and in many ways, in these last days has spoken to us in His Son, whom He appointed heir of all things, through whom also He made the world. And He is the radiance of His glory and the exact representation of His nature, and upholds all things by the word of His power.
So why then if the truth is revealed so clearly in Christianity is there so much variety in Christian doctrine? Perhaps more for my purposes here, how do I order what is true and understand it? For some, Christian truth is a bounded set, i.e. whatever lies inside of their circle of belief is orthodox and defines a real Christian, or at least who is the good guys. A centre bounded set is my preferred view; there are some key ideas (like the divine nature of Christ, his atoning death and resurrection, the Trinity, etc) and it is holding onto these that is key. There can be a lot of things on the periphery that we disagree on that doesn't disqualify us from fellowship, cooperation in ministry and so on. So for example I attend a church when those on staff are Calvinist but I am Arminian. We both agree God is sovereign but would disagree on how that sovereignty is exercised. And here is how I view these theological differences.
Imagine a quadrangle, an enclosed space encircled by many offices. There are trees, statues and a fountain in this quadrangle. Each different Christian tradition represents an office with a window view out onto this quadrangle. Some are high up, some are right down at ground level. All see the same scene but from different angles, and none of them see the entire view as one might from above. Some views don't show much of the quadrangle whereas some make more sense of the various features.
When I read a particular writer I don't agree with, we see the same scene from different angles. We might describe some of the main features but might not describe them in the same way, indeed in some cases one person's description might be unrecognisable to me. Other writers may describe a view that makes a lot more sense of the quadrangle than others and be more helpful to read.
This understanding allows me to read and listen to a variety of writers and still get some value out of them. To me, it is sometimes more important to focus on similarities even if I feel bound to argue over the differences. After all, we all live in the same building.