God is Holy means that He is far above any human being (Exodus 15:11; 1 Samuel 2:2). His holiness is perfect. Absolutely free from all sin, and pure. To be holy means being separated from fallen persons. God hates sin. His holy wrath must punish sin. Sinners can only approach the Holy God through the blood of Christ that washed away all sin (Isaiah 53:6). But just as he who called you is holy, so be holy in all you do; for it is written: “Be holy, because I am holy” (1 Peter 1:15-16).
God is Love does not mean that God loves (verb), but that He is Love (noun). 1 John 4:8 says: Whoever does not love does not know God, because God is love. Love is a desire for and a delight in the welfare for the one on whom love is given to. True love even loves sinners and enemies. But I tell you, love your enemies and pray for those who persecute you, that you may be children of your Father in heaven. He causes his sun to rise on the evil and the good and sends rain on the righteous and the unrighteous (Matthew 5:44-45). For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life (John 3:16).
God is Merciful means that He does not want to revenge, but rather forgives. The Lord is merciful and gracious, slow to anger and abounding in steadfast love (Psalm 103:8, ESV). After king David sinned (committed adultery) he wrote: Have mercy on me, O God, according to your unfailing love; according to your great compassion blot out my transgressions (Psalm 51:1). It is God's privilege and gift to show His mercy. For if the many died by the trespass of the one man, how much more did God’s grace and the gift that came by the grace of the one man, Jesus Christ, overflow to the many! (Romans 5:15b). Consequently, just as one trespass resulted in condemnation for all people, so also one righteous act resulted in justification and life for all people. For just as through the disobedience of the one man the many were made sinners, so also through the obedience of the one man the many will be made righteous (Romans 5:18-19).
God is Just means that He is righteous, fair and upright (Deuteronomy 32:4) and will dish out just judgment to every person. God cannot leave sin unnoticed nor unpunished. We all can know that God in His just judgment will always let His mercy prevail to those who deserve punishment but have a repentant heart. The apostle Peter said: I now realize how true it is that God does not show favoritism but accepts from every nation the one who fears him and does what is right (Acts 10:34-35).