Contradiction with Matthew 27:5
Judas, who betrays Jesus, ends his life, suggesting a loss rather than preservation.
Matthew 27:5: And he cast down the pieces of silver in the temple, and departed, and went and hanged himself.
Contradiction with John 17:12
Here, Jesus states that none were lost except the son of perdition, implying a contradiction in the preservation claim.
John 17:12: While I was with them in the world, I kept them in thy name: those that thou gavest me I have kept, and none of them is lost, but the son of perdition; that the scripture might be fulfilled.
Contradiction with Hebrews 6:4-6
This passage discusses the possibility of falling away, suggesting it is possible to be lost.
Hebrews 6:4-6: For [it is] impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost,
Contradiction with Matthew 7:21-23
Jesus declares that many will claim to know him but he will deny them, suggesting that some are indeed lost.
Matthew 7:21-23: Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven.