Why does God seem different in the Old Testament and the New Testament?

TL;DR:

God is unchanging. The God of the Old Testament is the same God of the New Testament, whose character and redemptive plan are revealed through His relationship with His people.

God may seem different in the Old Testament compared to the New Testament due to the different contexts in which He interacted with humanity, but He has not changed; His nature remains unchanged. In the Old Testament, God’s actions and judgments were often directed at nations and were necessary to establish Israel as a holy nation, demonstrating His justice and the seriousness of sin, yet salvation was still individual, as it is in the New Testament. The Old Testament set the stage with laws and covenants and demonstrated God’s nature and relationship with His people through the nation of Israel. Similarly, the New Testament focuses on the church demonstrating God’s nature and relationship with His people. Despite these contextual differences, God remains constant, revealing His unchanging nature and deepening our understanding of His redemptive plan.

from the old testament

God is unchanging (Exodus 3:14; Malachi 3:6). All the attributes of God, including His holiness, justice, love, mercy, grace, and omnipotence, are always present.
God promised a Savior (Genesis 3:15).
In Exodus 6:6–7, God promised to rescue Israel from slavery and make them into a nation called out for His purposes.
God provided the means for relationship with Him through the temple system (see Leviticus).
Leviticus and Deuteronomy are filled with God's expectations for the Israelites corporately: worship Him only (Exodus 34:14), observe the Sabbath (Exodus 16:29) and the feasts (Exodus 11 and 12; Deuteronomy 16:16; Leviticus 23:27–28), and follow His instructions without hesitation (Numbers 14).
In the Old Testament, God generally dealt with the Israelites as a nation, but He still had expectations for individuals. The most famous are those given in the Ten Commandments (Exodus 20:1–17).
God always responded with wrath and judgment against sin (Genesis 6–9; 18–19; Exodus 7–12; Joshua; 2 Kings, Jeremiah, Ezekiel). This judgment came both to nations and individuals. For example, Achan was killed in Joshua 7 for taking and hiding some of the devoted items from Jericho. God took David's son in response to David's adultery with Bathsheba (2 Samuel 12:15–23). And He kept Moses and Aaron from entering the Holy Land after their disobedience (Numbers 20:24; Deuteronomy 34:4).
Yet God always warned people of His coming judgment and provided a way to be rescued (the ark during the flood, warning Nineveh through Jonah, warning Israel through the prophets, giving the Canaanites 400 years to repent). God’s justice is always mixed with His grace and patience.
God's commands for Israel had to do with holiness and with living in ways that reflected who He is. For example, Micah 6:8 says, "He has told you, O man, what is good; and what does the LORD require of you but to do justice, and to love kindness, and to walk humbly with your God?"
We see God's compassion and tenderness throughout Scripture, such as in Genesis 16 and 1 Kings 17, where He gently cares for Hagar in her distress and provides miraculously for the widow and her son during a famine.
Jesus is foreshadowed in the Old Testament through prophecies, such as Isaiah 53, which describes the suffering servant, and through types and symbols, like the Passover lamb in Exodus 12:21–27, which points to His sacrificial death. He also appears in theophanies, such as the "Angel of the Lord" in Genesis 16:7–13.
The Holy Spirit existed in the Old Testament. He occupied the centralized worship center of a chosen nation (Exodus 40:34) and was promised to occupy every believer's heart at a future time (Ezekiel 36:26–27; Joel 2:28–29).

from the new testament

God is unchanging. This is repeated in the New Testament (John 1:1–4; James 1:17–18; Hebrews 13:8). All the attributes of God are present in the Old Testament and in the New.
God came as the ultimate Savior (John 3:16).
The Exodus where God delivered His people from Egypt became the living example of God rescuing people from sin and calling them to be His people as a light to the world (Matthew 5:14–16; 1 Peter 2:1–12).
The temple system, where man could be in relationship with God, was ultimately fulfilled in Jesus (see Hebrews).
The New Testament also contains instructions for the new corporate body—the church. The church is not to harbor unrepentant hearts (1 Corinthians 5:1–2) but to follow a detailed set of instructions to purge itself of sin (Matthew 18:15–20).
Matthew 5 gives several expectations for individuals in the church age, including the admonishment to do whatever is necessary to keep oneself from sin (vs. 29–30).
In the New Testament, God revealed His wrath and judgment against sin as well. Jesus spoke extensively about the coming judgment and the consequences of failing to live according to God’s standards (Matthew 5–7, 23). Jesus foretold the destruction of Jerusalem as a consequence of the city's rejection of Him and its failure to recognize the time of its visitation (Matthew 24; Luke 21). The Book of Revelation describes various judgments and plagues that will come upon the Earth in the end times. Revelation 20:11–15 tells us of the final judgment, where those whose names are not found in the Book of Life are cast into the lake of fire. This is the ultimate expression of God’s judgment against sin.
Just as God held individuals accountable for their sin in the Old Testament, so in the New Testament, Ananias and Sapphira were struck down after lying about their offering (Acts 5:1–11), and Jesus rebuked Peter when Peter denied Jesus's purpose (Mark 8:31–33).
God’s justice and patience to execute justice are seen in the New Testament as well. In Revelation, we see that people know that the judgments are from God, yet they refuse to repent (Revelation 9:20–21). Second Peter 3:9–11 assures us that God wants all to come to repentance, so He is patient, giving people time to respond to His warnings.
God’s call to live in ways that reflect who He is (John 13:34–35; Ephesians 4:25–32; James 1:27; 1 Peter 1:13–25) is in line with the Old Testament.
God’s compassion and tenderness are also seen in Luke 7 and 1 Peter 5:7, where Jesus raises a widow's son with deep compassion and invites us to cast all our anxieties on Him because He cares for us.
In the New Testament, Jesus takes on human flesh through the incarnation, as described in John 1:14, "The Word became flesh and dwelt among us." This is further affirmed in Philippians 2:7–8, where it says that Jesus became fully human, obedient to death on a cross.
With the resurrection and ascension of Jesus, the role of the Holy Spirit changed to accommodate the context. Instead of limiting His direct involvement to a few prophets, priests, and kings, He now indwells and counsels every believer (1 Corinthians 6:19).

implications for today

God is the same yesterday, today, and forever. This unchanging nature of God means that His character, promises, and expectations remain constant across all time. We are invited to know this unchanging God and to respond to His offer of salvation. The same God who created the earth made the way for us to be forgiven of our sins and to have abundant life, now and for eternity (John 10:10). God hasn't changed; the context has changed. God's holiness, passion, restraint, and judgment are all the same; we just see it on a personal level instead of a national one. This personal experience of His love and forgiveness means that no matter where we are or what we've done, we can always find in Him the unwavering grace and unending hope that transforms our lives and guides us toward an eternal future with Him.

understand

God's character is constant throughout both Testaments.
God consistently calls His people to a relationship with Him and to obedience.
The promise of a Savior in the Old Testament is fulfilled in Jesus Christ in the New Testament, demonstrating a continuous plan of redemption.

reflect

How does understanding that God’s character is consistent across the Old and New Testaments influence your view of His promises and nature?
How have you personally experienced God’s call to relationship and obedience, and how does this reflect His unchanging nature?
How does knowing that God's redemptive plan spans both Testaments impact your understanding of His work in your life?

engage

God often appears different between the Old and New Testaments because He dealt with people on different levels: more nationally in the Old Testament and individually in the New Testament, although He still works nationally now and dealt with people individually in the Old Testament. Although the contexts differ, God's consistent character—His holiness, justice, and desire for righteousness—remains unchanged across both Testaments, and the way He worked in these contexts was for the same plan of redemption.
How does the consistency of God's justice and mercy across the Testaments shape our understanding of His actions in Scripture?
How should the shift from a national to a personal focus in God’s dealings influence our approach to individual and communal faith today? How can we uphold both the communal and individual aspects of our faith?