Many people argue that because salvation is a “free gift,” that humans do nothing to earn it, and therefore can do nothing to lose it.
Whoever believes in the Son has eternal life, but whoever disobeys the Son will not see life, but the wrath of God remains upon him. John 3:36 NAB
Now I would remind you, brothers, of the gospel I preached to you, which you received, in which you stand, and by which you are being saved, if you hold fast to the word I preached to you—unless you believed in vain. 1 Cor. 15:1-2 ESV
“How can they be worse off if they received something that can never be taken away from them?”
20 For if, after they have escaped the defilements of the world through the knowledge of our Lord and Savior Jesus Christ, they are again entangled in them and overcome, the last state has become worse for them than the first. 21 For it would have been better for them never to have known the way of righteousness than after knowing it to turn back from the holy commandment delivered to them. 22 What the true proverb says has happened to them: “The dog returns to its own vomit, and the sow, after washing herself, returns to wallow in the mire.” 2 Peter 2:17-22 ESV
Most born-again Christians would become lost again:
“God had foreseen… that faith even after baptism would be endangered. He saw that most persons after attaining unto salvation would be lost again by soiling the wedding dress, by failing to provide oil for their torches.” ~ Tertullian (c. 213)