The sacred command (or holy commandment, KJV) mentioned only once in Scripture is another Bible mystery. According to Peter, former Christians turn their back on the sacred command when they go back to sin. The one and only Scripture, which actually mentions by name the sacred command, is this one:
If they have escaped the corruption of the world by knowing our Lord and Savior Jesus Christ and are again entangled in it and overcome, they are worse off at the end than they were at the beginning. It would have been better for them not to have known the way of righteousness, than to have known it and then to turn their backs on the SACRED COMMAND that was passed on to them. Of them the proverbs are true: “A dog returns to its vomit,” and, “A sow that is washed goes back to her wallowing in the mud.” (2 Pet 2:20-22)
Maybe 1 John 3:23 Is The Sacred Command
What could that mysterious sacred command be, which apparently Christians have been given? Because there is NO Scripture which the sacred command is directly connected to, we can only guess. However, there is one passage which singles out one command over all the many commands! It also seems to fit the description of the sacred command and how it is violated by backsliders.
And this is his command: to believe in the name of his Son, Jesus Christ, and to love one another as he commanded us. (1 John 3:23)
In that verse, the word believe is synonymous with obey. Hence, if one backslides, as the ones in 2 Peter 2 did, then he has also turned his back on obeying (believing on Jesus) and the sacred command too! Maybe that solves this Bible mystery.