Francis Turretin’s Institutes of Elenctic Theology contains a very helpful section on the differences between essential vs. non-essential doctrines. In article XXII of this section, Turretin makes a very important distinction between adhering to “words” vs. adhering to the “sense”, or meaning, of words. Why is this important? Because false teachers and others who seek to disrupt the church will often tell you that they affirm the same doctrines you do but in reality, once you dig deeper and find out what they actually mean by what they believe, it is altogether different.

Full Preterists, for example, have no problem telling you that they believe in the second coming of Christ, the resurrection of the body, the final judgment, and so on. But when you ask them to explain what these doctrines mean, you will discover something totally repugnant to sound, historic, Christian faith. They affirm the words used of the Christian faith, but in actuality deny the Christian faith. Do not fall for their trap.

…the Symbol {Apostles’ Creed} is not to be considered only with regard to the words, but as to the sense (because, as Hilary says, “The Scriptures do not consist in the reading but in the understanding,” Ad Constantium Augustum, II,9 [PL 10.570]; and “fundamentals are not found in the words but in the sense,” as Jerome says). Therefore although heretics may say that they receive the Symbol, yet they do not because they reject its true and genuine sense. So Sabellius, Arius, Macedonius and other anti-Trinitarians formerly professed (to no purpose) in the words of the Symbol their faith in the Father, Son and Holy Spirit, while they endeavored to overthrow this very doctrine not by secret attacks, but by open warfare. The Socinians of our day and their disciples are doing this. In vain do the papists profess their belief in it, who corrupt the meaning of the various articles concerning the sufferings and death of Christ, his descent to hell, the catholic church, the remission of sins and the like.

~ Francis Turretin, Institutes of Elenctic Theology, Vol. 1, pg. 53.

One practical thing to be learned from this is that the next time someone tells you that they are a “Christian” or “Reformed” or whatever, do not stop merely at their words. Ask them to explain what is meant. You just might save yourself a headache.