There are some blunt, tell-it-like-it-is passages in the Bible. One that comes to mind is 1 John 2:19 – “They went out from us, but they were not of us; for if they had been of us, they would have continued with us.” (ESV)
This is not merely a historical recounting by John, but a warning for us today: We must resist defining Christianity as anything other than a deep devotion to Christ, the fruit of which is a lifestyle of daily worship of him and active service in his kingdom.
We must always be evaluating the motivation of our hearts to be sure that the faith we live by is the true Christianity of the Bible, not an externalistic counterfeit that omits Jesus.