Contrary to Scripture, the modern gospel assures people that if they sincerely pray a “sinner’s prayer,” they should never doubt their salvation. Some go so far as to say that any doubts are from the devil. With eternity at stake, however, Paul admonishes believers to test themselves to make sure their faith is sound and secure.
Think of what you would do if you were wearing a parachute and waiting to jump out of a plane. You would have faith in the parachute, but you would also regularly check to make sure that the straps are firm. Once you have put on the Lord Jesus Christ through conversion (repentance and faith), you should regularly examine yourself to see how firm your relationship is with the Lord. Are you reading the Word daily? Do you have regular prayer? Are you fighting sin, or giving in to it? Are you living in holiness? Are you confessing sin? How is your relationship with other Christians? Is there any hidden bitterness against anyone? Are you sharing your faith? What is your greatest passion? Is it the Lord, or are material things more important? Do you love the world and the things in the world? On a scale of one to ten, how would you rate your walk with God? It should be a ten. If it is not, strive to make it a ten.
2 Corinthians 13:5 Examine yourselves as to whether you are in the faith. Test yourselves. Do you not know yourselves, that Jesus Christ is in you?—unless indeed you are disqualified.
Bottom line: If you’re talking the talk ( claiming to be a Christian) but not walking the walk ( acting like a sinner), you should take the advice of 2 Corinthians 13:5.
The context of the verse 2Cor. 13: 5 of 2Cor. 12: 21 where Paul bewails the Christians who have not changed their Mind ( repented-Strong’s Concordence) of their sin. Reprobates(2 Cor. 13:5) in this context means unapproved worthless. It is involved in the sanctification issue not a salvation issue.