"You have heard that the ancients were told, ‘You shall not commit murder’ and ‘Whoever commits murder shall be liable to the court.’ But I say to you that everyone who is angry with his brother shall be guilty before the court; and whoever says to his brother, ‘You good-for-nothing,’ shall be guilty before the supreme court; and whoever says, ‘You fool,’ shall be guilty enough to go into the fiery hell." (Matthew 5:21-22)
"You have heard that it was said, ‘You shall not commit adultery’; but I say to you that everyone who looks at a woman with lust for her has already committed adultery with her in his heart." (Matthew 5:27-28)
The context of this passage from the Sermon on the Mount is about adhering to the spirit of the law, not just the letter. God does not only examine behavior, but also the heart. People practice various sins because their hearts are already dedicated to unrighteousness. Our deeds are the evidence of our current spiritual state. Folks like King David did not "practice" adultery and murder, but got ensnared by those sins during a period of spiritual vulnerability.
God disciplines those who He loves, just as a father does a son who is guilty of some wrongdoing (Deuteronomy 8:3-5; Proverbs 3:12). A God who is willing to lay down His life for sinners is not going to instantaneously give up on somebody. That is totally unrealistic. A person does not reach sinless perfection upon conversion. We still struggle with a sin nature, but the grace of God, which we do not deserve, does transform our hearts. How God dealt with Israel in the Old Testament is a testimony to His patience. King David himself serves as a display to the greatness of His mercy.
The loss of salvation is not caused by a single bad work, but is a slow, gradual process that takes place over time. We do not do bad works to "get unsaved." Bad works are the evidence, not the cause, of a declining faith or hardening heart. Our works are symptomatic of our spiritual state. God examines our hearts. We are justified by faith, apart from the merit of any good works (Romans 4:2-8). We are saved by faith in Christ and His gospel. We obtain mercy from God through heartfelt repentance.
It is technically difficult for a Christian to lose his or her salvation. God is slow to anger (Psalm 145:8). He is rich in mercy (Ephesians 1:7-8). He does not will that any man perish (2 Peter 3:9). He is faithful even during our times of unfaithfulness. The Holy Spirit continually convicts the conscience of sin. But He can still cast off bad branches. Christians do not lose their free will upon conversion. People can and do, though as shocking or unfortunate it may seem, abandon heartfelt convictions. God forbid that a believer apostatize from the faith, but it is an undeniable reality. He certainly has the power to keep us, but will not force people into heaven. That would not be love. We were not created to be robots or puppets, but His children.
If a Christian holds fast to the gospel by faith, and that alone, then he or she can rest assured of entering Paradise in the afterlife. We are kept in by the Holy Spirit in the same way that we entered the Kingdom of God: faith (Galatians 3:1-6; Colossians 2:6-7). In other words, we are both justified and sanctified by faith. Justification is not like some sort of a wage that we can deplete by sin. We are either fully a part of God's kingdom or not a member at all. There is no in-between. Belief in eternal security is not by any means a requirement for subscribing to Sola Fide. David J. Stewart also made this problematic statement in his article:
"I am going to Heaven, regardless of how I live. But you say, that's crazy! No! That's Bible!"
The above quoted excerpt is contrary to everything that Scripture teaches concerning sanctification in the Spirit. It actually proves the author being critiqued to be a false teacher, as he openly and boldly promotes a license for immorality. Such is an utter disgrace to the Cross of Christ. Contrast the words of David J. Stewart with the Apostle Paul's words in Romans 6. Ironically, Mr. Stewart derisively condemns just about everybody who disagrees with him even on the smallest of matters. His overall mentality lacks consistency and is despicable.
If the lives of Christians are characterized by sin and display not even the slightest desire for repentance and growth in sanctification, then yes, they have sufficient reason to question the validity of their profession of knowing God personally.
Let it be said that it is indeed possible for one to lose salvation, as Scripture passages such as 1 Corinthians 15:2, 1 Timothy 4:16, 2 Timothy 1:14 and many other texts plainly attest. We are not called to sit back and relax. There are no passages in Scripture exempting Christians from the consequences of sin. Notice that God said in the Old Testament of certain Jews that if they continued in their rebellion against Him, He would "love them no longer" (Hosea 9:15). There is nothing we can do to merit our salvation. God's Law demands perfect obedience. Yet, we have all sinned. That is why mankind has incurred His condemnation. At the same time, God the Father out of His unfathomable love for us sent God the Son into the world to make atonement for our sin. We must place our trust in His work alone for justification. We can indeed have great assurance of salvation. It is a present tense possession. It is not as though we have to wring our hands every time we make a mistake or be in constant fear. We all have fallen short of God's glory. We are all liable to error. But we should never put off repenting.
There is no opportunity for boasting in the Christian life because justification is by faith alone (Ephesians 2:8-9; Titus 3:4-7). It is not devoid of good works, but evidenced by good works (Ephesians 2:10). A saving faith is accompanied with a desire to know and serve God. We are saved only by the blood of Jesus Christ. Justification does change a person. The Holy Spirit keeps us in the kingdom of God by the same way that we entered, faith. But we must make a choice to be saved. We are responsible for our stay here on earth. We who profess Christ need to periodically examine ourselves in light of God's Word (2 Corinthians 13:5).