Faced with so many denominational differences and interpretations, how can someone determine what the real message of the Gospel is?
It is a fair question.
Is there a fair answer?
The primary principle is simply to read the Bible as God had it written. That means reading the Scriptures carefully and with deliberation. Look at ...each verse..., ...each phrase..., ...each word... and ...each passage..., without rushing, slowly. See what they actually say. Note any differences between what they say and what we thought (had been taught) they meant. Note how some of them must be interpreted to line up with the established doctrine you are used to.
Also note any apparent inconsistencies between different verses, passages, etc., and any verses that seem internally inconsistent when looked at closely.
Just doing that should have people scratching their heads before too long.
Keeping a list of passages, verses, phrases and words that seem troublesome, including verses that may contain internally conflicting statements, or that apparently conflict with others, is a great idea. It may all seem confusing at first, because thoughts contrary to denominational doctrine might be encountered. But later on, the things you have noted will mesh with new things you are finding, to form a mosaic more beautiful than you ever could have imagined.
It is definitely worth the effort.
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A subsequent post will contain a few secondary pointers which can help people detect and deal with poor (and sometimes biassed) translation, and the hard-to-shake pre-conditioning we have all been subjected to.