ANTINOMIANISM (Against/Without Law)
When discussing about the above to a Catholic, Jehovah's Witness, LDS, Fundamentalist Church of Christ, etc, they will point to examples of Christians who lost their salvation, as well as Pastor caught in adultery, etc. To them, believing in the above doctrines will allow Christians to live like the Devil for no matter what they do, they'll never lose their salvation.
TRUE BELIEVERS
Biblically however, their worries are unfounded:
1. When they're saved they acquired a new nature (2 Corinthians 5:17)
2. They, are no longer slaves to sin but righteousness (Romans 6:16-18)
3. While it is always possible for them to backslide, they will not long tarry in it (1 John 3:6-9)
4. Christ who have saved them will Finish the work He had begun in them (Ephesians 2:10 & Philippians 1:6)
5. And should they backslide the Lord will chastise them (Hebrews 12:6-8) & if they sinned to such a level, they will be given over to Satan to be buffeted by him so that by adversity s/he will return (1 Corinthians 5:5). Recall King Nebuchadnezzar (Daniel 4:19-37) & the Parable of the Lost Son (Luke 15:11-24)
FALSE BELIEVERS
There are true believers & then there are false believers (1 Corinthians 15:1-3). False believers can claim to be Christian, walk in the Lord for a time, but the same will not long endure a believer's life.
These are the same exemplified in the Parable of the Sower (Matthew 13:18-23) that while they initially receive the truth joyfully, when they're confronted w/ their sin(s) (Matthew 18:15-18), faced w/ adversity, or persecution arises then they will depart from the faith & will never return (1 John 2:15-16).
FOR THE UNSURE
If you're in a state uncertain whether you're saved or not, the Bible says to test & examine yourself whether you truly believe (2 Corinthians 13:5).
Ask yourself do you truly hate sin? Are you living a life of repentance? Is it unthinkable to you to leave Christ gladly? If you say Yes, Yes, & No then it is evidence that you are saved. If it is the reverse, then you'll need to worry.
However, the fact that you are doubting your salvation, checking your motives is further evidence that you are saved.
But if righteousness is nothing more than "bad (tasting) medicine" that you have to take just to be safe, or weekly church service an obligation to you, then you might not be saved after all.
Make sure that you truly believe (2 Peter 1:10).