The same God runs through both Testaments
The Bible itself says that God does not change (Malachi 3:6). Jesus is also described as unchanging (Hebrews 13:8). So the contrast can feel real, especially when reading stories of war, exile, and judgement in Israel's history, but Scripture does not ask us to imagine two different Gods.
In the wilderness, after Israel had made the golden calf, God revealed Himself to Moses as compassionate, gracious, patient, loving, and faithful. In that same moment, He also made clear that evil matters to Him and will not simply be ignored (Exodus 34:6-7). Mercy and justice were never opposites in God's character.
And the Lord passed by before him, and proclaimed, The Lord, The Lord God, merciful and gracious, longsuffering, and abundant in goodness and truth,
The Old Testament is full of mercy
It is easy to remember Pharaoh, Jericho, or Israel's exile and miss the long patience surrounding those events. God sent prophets to call His people back over generations. Through Ezekiel, He said He took no pleasure in the death of the wicked, but wanted them to turn and live (Ezekiel 33:11).
David knew both God's correction and His kindness. After his own serious sin, he appealed to God's abundant mercy (Psalm 51:1). Another psalm says that God is compassionate and does not deal with His people as their sins deserve (Psalm 103:8-10). The Old Testament does not hide judgement, but it repeatedly shows God seeking repentance before judgement falls.
The Lord is merciful and gracious, slow to anger, and plenteous in mercy.
The New Testament still speaks of judgement
Jesus welcomed outcasts, healed the suffering, and forgave sinners. He also warned plainly about hypocrisy, greed, hard-heartedness, and coming judgement (Matthew 23:23; John 5:28-29). His love was never casual about what destroys people.
The apostles carry that same note. Paul tells the divided church in Corinth that all people will stand before Christ's judgement seat (2 Corinthians 5:10). Revelation portrays God judging evil and setting things right (Revelation 20:12). The New Testament's good news is not that justice has disappeared. It is that God has acted in Christ to rescue sinners.
Jesus shows what God is like
Jesus did not come to cancel the Old Testament God. He said His mission fulfilled the Law and the Prophets rather than discarded them (Matthew 5:17). He spoke of the Father as merciful, then showed that mercy by eating with sinners, touching lepers, and giving His life for others (Luke 6:36; Mark 10:45).
At the cross, God's love and justice meet. God demonstrates His love for sinners through Christ's death, while Christ bears the consequences of sin rather than pretending sin is harmless (Romans 5:8; 1 Peter 3:18). That is why Christians look to Jesus when difficult Old Testament passages raise questions. He is not a softer alternative to God. He is the clearest revelation of God.
Who being the brightness of his glory, and the express image of his person, and upholding all things by the word of his power, when he had by himself purged our sins, sat down on the right hand of the Majesty on high;
Keep reading the whole story
Some passages remain difficult. Faithful Christians have wrestled with them for centuries, and quick answers can flatten real pain or complexity. Try reading a troubling story in its wider setting: what had happened before it, what God had said through His prophets, and how the Bible's story leads towards Jesus.
The central thread is steady. God is holy and opposed to evil, yet rich in mercy towards people who turn to Him. Jesus invites us to know the Father through Him, not to be afraid of asking honest questions along the way (John 14:9).