Is it unloving to tell another person he/she is sinning?

TL;DR:

It is not unloving to tell another person he or she is sinning. Instead, it is unloving to ignore sin because it leads to destructive consequences. However, we must make sure that we speak the truth in love and that we address sin with gentleness, respect, and the goal of restoration.

what does the bible say?

It is not unloving to tell someone they are sinning; ignoring sin is more harmful because it leads to destruction. In the Old Testament prophets confronted sin with the goal of calling people to repentance, and the New Testament also shows people calling out sin with the focus of restoring believers and pointing unbelievers toward Christ. Confronting sin should be done with gentleness, respect, and love, focusing on helping others experience life in Christ. Modern culture confuses love with tolerance, but true love seeks to prevent harm and guide others toward God’s truth. We are called to encourage one another toward righteous living and restoration.

from the old testament

The Old Testament includes several instances where people were called out for their sin. After David's sin with Bathsheba and the murder of Uriah, God sent the prophet Nathan to confront David. Nathan used a parable about a rich man who took a poor man's only lamb to illustrate David's wrongdoing. When David realized the parable applied to him, Nathan called him to repentance, and David acknowledged his sin, seeking God's forgiveness (2 Samuel 12:1-15).
After King Ahab and Queen Jezebel orchestrated the murder of Naboth to take his vineyard, the prophet Elijah confronted Ahab. Elijah declared God's judgment on Ahab and his house but also called Ahab to repentance. Ahab humbled himself before God, and his repentance delayed the judgment for a time (1 Kings 21:17-29).
The prophet Isaiah delivered God's message to the people of Judah, calling them to repent of their evil deeds and return to justice. God offered forgiveness if they would "wash themselves" and "cease to do evil," inviting them to reason together and seek repentance to avoid judgment (Isaiah 1:16-20).
The prophet Jeremiah called the people of Israel to return to the Lord (Jeremiah 3:12-14).
Hosea called Israel to repentance, urging them to return to the Lord. He emphasized that their transgressions had led to God's anger, but if they would seek the Lord earnestly, they would find healing and restoration (Hosea 6:1-3).
The prophet Amos denounced Israel's sinful behavior and called them to repentance. He urged them to “seek good and not evil” so that they might live and avoid God's judgment (Amos 5:14-15).

from the new testament

Sin separates people from God. Romans 6:23 says that "the wages of sin is death."
Apart from Christ, we are condemned to an eternity separated from God in hell. But, "God so loved the world, that he gave his only Son, that whoever believes in him should not perish but have eternal life. For God did not send his Son into the world to condemn the world, but in order that the world might be saved through him" (John 3:16-17).
Even for those who already know Christ—whose sins have been forgiven and whose eternities are secure—sin still separates us from God. First John 1:8-9 says, "If we say we have no sin, we deceive ourselves, and the truth is not in us. If we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness." Sin causes a relational distance between us and the source of true life. Telling someone they are sinning is a loving act to help restore them to God.
In the case of unbelievers, specific sins are not the issue—not having a relationship with God through Jesus is. God does not want unbelievers to "clean up their act." He wants to give them new life through Christ. All people need to recognize that we are sinners (Romans 3:23), that sin brings death (Romans 6:23), and that the only means of forgiveness and life is through Jesus (Ephesians 2:8-9).
Confronting sin in unbelievers is really about sharing the gospel message. We need not concern ourselves with specific sins, but with the overall call from death to life. Paul does this in 1 Corinthians 5:9-13. Behavior modification in unbelievers is not our goal. Sharing the good news of forgiveness and life in Jesus is.
Believers are meant to help one another live the Christian life. Jesus has called us to obey Him. In doing so we bring glory to God and bear fruit that will last. It is by obedience that we abide in Christ and can fully experience His love and joy (John 15:1-17). When we help other believers who are in sin—and remain open to others helping us when we are in sin—we are helping one another live the life God intended for us.
The goal in confronting sin in believers is the same as for unbelievers: helping people experience life in Christ. But with believers , we bring up specific sins. James 5:19-20 says, "My brothers, if anyone among you wanders from the truth and someone brings him back, let him know that whoever brings back a sinner from his wandering will save his soul from death and will cover a multitude of sins."
Galatians 6:1 also says, "Brothers, if anyone is caught in any transgression, you who are spiritual should restore him in a spirit of gentleness. Keep watch on yourself, lest you too be tempted." We raise our concerns with fellow Christians because we want to help them experience the fullness of the life God has for them.
The writer of Hebrews instructed, "But exhort one another every day, as long as it is called 'today,' that none of you may be hardened by the deceitfulness of sin" (Hebrews 3:13). James 5:16 says, "Therefore, confess your sins to one another and pray for one another, that you may be healed." Telling another believer about sin in their lives should not be about pride; it should not be done in an effort to control them or to humiliate them. Rather, it should be done from a heart of love, a heart that desires to encourage, a heart that is also open to correction.
Even if we confront sin in the life of another believer, we do not need to call out every sin in a person. First Peter 4:8 says, "Above all, keep loving one another earnestly, since love covers a multitude of sins." First Corinthians 13:4-7 says, "Love is patient and kind; love does not envy or boast; it is not arrogant or rude. It does not insist on its own way; it is not irritable or resentful; it does not rejoice at wrongdoing, but rejoices with the truth. Love bears all things, believes all things, hopes all things, endures all things." When a person’s sin impacts others, is detrimental in their own life, or is a repeated pattern, we can pray for how to lovingly address it.
Even Jesus did not point out people's every sin. Rather, He came "full of grace and truth" (John 1:14). He did not shy away from confronting sin, but always did so with love and pointing toward God's forgiveness and grace.

implications for today

Modern culture tells us that to disagree with others is to inappropriately judge or condemn them. We are taught to be "tolerant," meaning we should accept and affirm what people do. We are told that people have different "truths," and what is right for some may not be right for others. That viewpoint says if we disagree or think others are sinning, then we don't love them; and to voice our opinion would be unloving. But is that really love? If we know a person is about to walk off the edge of a cliff, yet he seems happy to be doing so, is it loving to allow him to continue? Confronting sin in another person is difficult, and unfortunately it is often done in a very unloving manner. But ignoring sin is not loving.

At the same time, though it is loving to tell someone that they are sinning, there are loving and unloving ways to go about it. The Bible tells us that our words should be seasoned with salt and that they are to impart grace (Colossians 4:6). We are to speak the truth in love (Ephesians 4:15) and to give defenses of our faith with gentleness and respect (1 Peter 3:15).

We are not the sin police. Our job is not to convict others about what they are doing. Our job is to care for one another enough to point out blind spots and journey together in the process of restoration. We should also "consider how to stir up one another to love and good works, not neglecting to meet together, as is the habit of some, but encouraging one another, and all the more as you see the Day drawing near" (Hebrews 10:24-25). In love, we do not just point out sin; we encourage one another toward righteous living. It is not unloving to tell others they are sinning. In fact, helping restore others to a right relationship with God is one of the most loving things we can do.

understand

It's not unloving to point out sin; ignoring it is.
When telling someone that he or she is sinning, we need to speak the truth in love, with gentleness and with the goal of restoration.
Confronting sin helps restore relationships with God and leads to abundant life.

reflect

How do you approach confronting sin in your own life, and how does that impact how you approach sin in another person’s life?
Have you ever hesitated to point out sin in someone else's life? What could motivate you to address it with gentleness and respect?
What can you do to ensure that your actions and words toward others promote restoration rather than judgment or condemnation?

engage

How can we confront sin without falling into pride or self-righteousness?
Why is it important to focus on restoring relationships with God rather than merely correcting behavior in others?
What are some practical ways to speak the truth in love, especially when addressing sensitive or painful topics like sin in a person’s life?