Eternal Security (Once saved alway saved)
Eternal Security is found in the Bible, which promises that salvation is secured by God, not by human effort. These verses declare that believers cannot lose their salvation. (John 5:24, Philippians 1:6, John 6:37-39, 1 Peter 1:5)
John 10:27-29: “My sheep hear my voice, and I know them, and they follow me; and I give them eternal life, and they shall never perish, and no one shall snatch them out of my hand. My Father, who has given them to me, is greater than all, and no one is able to snatch them out of the Father’s hand.”
Romans 8:38-39 “For I am sure that neither death, nor life, nor angels, nor principalities, nor things present, nor things to come, nor powers, nor height, nor depth, nor anything else in all creation, will be able to separate us from the love of God in Christ Jesus our Lord.”
Ephesians 1:13-14 “ In him you also, who have heard the word of truth, the gospel of your salvation, and have believed in him, were sealed with the promised Holy Spirit, which is the guarantee of our inheritance until we acquire possession of it, to the praise of his glory.”
The question/problem: There are Christians who have lived their life for God, then change and depart from their faith. Some even depart into a very sinful lifestyle. Are they still saved? This is a paradox (an apparent contradiction). But there are a few solutions.
The person could be like David of the Bible, a man after God's own heart (Acts 13:22). Though David sinned greatly, later he repented and returned to God. This is also the parable of the prodigal son (Luke 15:11-32). (yet David was not permitted to build the Temple due to his sins)
If the believer does not come back, they are still saved, but they will receive fewer rewards in this life and the next. (2 Tim 4:8, Rev 2:10, Gal 5:22-23, rewards are not physical things, but joy, peace, wonder and a like.)
The person was never saved in the first place. Matthew 7:21-2: “Not every one who says to me, ‘Lord, Lord,’ shall enter the kingdom of heaven, but he who does the will of my Father who is in heaven. On that day many will say to me, ‘Lord, Lord, did we not prophesy in your name, and cast out demons in your name, and do many mighty works in your name? (These are people trusting their good works, as listed here. But good works will get no one into heaven, Romans 3:10, Ephesians 2:8-9).
Hebrews 6:4-6 (debated on this topic as written to the Jews at that time). For it is impossible to restore again to repentance those who have once been enlightened, who have tasted the heavenly gift, and have become partakers of the Holy Spirit, and have tasted the goodness of the word of God and the powers of the age to come, if they then commit apostasy, since they crucify the Son of God on their own account and hold him up to contempt. The question is, can one taste the goodness of Christian fellowship and enjoy it, but never have a saving faith in Christ, by still trusting in one's works, or a different god (apostasy).
The warning and instructions to those asking the question-paradox of Eternal Security: 1 Samuel 16:7b: “People look at the outward appearance, but the Lord looks at the heart.” (also see Proverbs 21:2 and Sermon On The Mount (Mat 5:3-14) : God knows each person's motives and heart, we do not).
Matthew 7:1-5, and Romans 2:1, tell us to use care in judging others. (As we only see the outside, not the heart. We are sinners also, in need of forgiveness too.
Galatians 6:1 “Brethren, if a man is overtaken in any trespass, you who are spiritual should restore him in a spirit of gentleness. Look to yourself, lest you too be tempted.”
Ephesians 4:15a: “Instead, speaking the truth in love”