Answer: Many Christians use the cliché “Love the sinner, hate the sin.” However, we must realize that this is an exhortation to us as imperfect human beings. The difference between us and God in regard to loving and hating is vast. Even as Christians, we remain imperfect in our humanity and cannot love perfectly, nor can we hate perfectly (in other words, without malice). But God can do both of these perfectly, because He is God. God can hate without any sinful intent. Therefore, He can hate the sin and the sinner in a perfectly holy way and still be willing to lovingly forgive at the moment of that sinner's repentance and faith (Malachi 1:3; Revelation 2:6; 2 Peter 3:9).
The Bible clearly teaches that God is love. First John 4:8-9 says, “Whoever does not love does not know God, because God is love. This is how God showed his love among us: He sent his one and only Son into the world that we might live through him.” Mysterious but true is the fact that God can perfectly love and hate a person at the same time. This means He can love him as someone He created and can redeem, as well as hate him for his unbelief and sinful lifestyle. We, as imperfect human beings, cannot do this; thus, we must remind ourselves to “love the sinner, hate the sin.”
How exactly does that work? We hate sin by refusing to take part in it and by condemning it when we see it. Sin is to be hated, not excused or taken lightly. We love sinners by being faithful in witnessing to them of the forgiveness that is available through Jesus Christ. A true act of love is treating someone with respect and kindness even though he/she knows you do not approve of his lifestyle and/or choices. It is not loving to allow a person to remain stuck in sin. It is not hateful to tell a person he/she is in sin. In fact, the exact opposites are true. We love the sinner by speaking the truth in love. We hate the sin by refusing to condone, ignore, or excuse it.
Recommended Resource: The Difficult Doctrine of the Love of God by D.A. Carson.