How do those Christians who believe that the personal salvation once received by an individual by believing unto Christ and turning to Him in a prayer cannot be lost explain Matthew 7:19-23?:

Every tree that bringeth not forth good fruit is hewn down, and cast into the fire. Wherefore by their fruits ye shall know them. 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. Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works? And then will I profess unto them, I never knew you: depart from me, ye that work iniquity. (Matthew 7:19-23, KJV)

It looks like this passage tells us of people who knew the Lord's name and did pray to Him in their lifetime. They even used the Lord's name to cast out demons. That is, most likely, they were saved. However, they seem to fall into a category of those who are cast into fire.