Satan's great deception! Once saved always saved?

I'm not the first to expose the false doctrine. As long as there are believers being seduced and deceived by this lie I must be a watchman and sound the alarm to warn you and hopefully help you to preserve your soul. Scripture is clear on this matter.
Many verses warn us that we can lose our salvation and YHWH's favour if we turn away from doing his will and return to the world and to sin after learning the truth about the gift of mercy and salvation that he offers us. Let's see what the bible says about this doctrine and prove it to be false once and for all.