God's pattern of judgment and grace all started with Adam and Eve. They fell into disobedience to God. They were banned from the Garden of Eden.
Things kept getting progressively worse. Individuals and cities were judged. God brought the flood of Noah to wipe out the entire population of the earth except for 7 people in Noah's immediate family.
God judged the Egyptians with plagues because Pharoah would not let the Israelites go free. After they were finally freed and God opened up the Red Sea to permit them to continue their journey from the pursuing Egyptian army, he judged them for disobedience and whining in the wilderness.
All through the Old Testament we see where God judged individuals, nations, governments, and raised up or dethroned leaders. This continued for thousands of years.
About 2000 years ago God sent his son, Jesus, to show people their need for a Savior. He died on a cross and rose again from the grave for man's salvation, and to make it possible for us to avoid future judgment. This also ushered in the age of grace.
Many people have still refused to obey God's way and have turned away from him. Grace does not mean we can live any way we want to. There is still judgment in the midst of grace. God is still judging people, nations, governments, and leaders.
All of this shows the sinfulness of the human heart. For the past 2000 years people still have not heeded God's ways, so judgment is coming again. We are already beginning to see it. At some point in the future we are going to see God's judgment poured out upon the earth in many ways, one of which will be plagues. It happened before, as was mentioned earlier when Pharoah refused to allow the Israelites to be free from bondage. God will do it again, but this time it will upon the entire earth. These plagues are mentioned in Revelation 16. Notice the similarity between the plagues in Exodus and the ones listed in Revelation. It will happen literally just like it happened literally in the Old Testament times.
The Exodus account reveals that water turned to blood, frogs overcame the land, there were swarms of insects, pestilence came upon livestock, people experienced boils and sores, hail came down from heaven, God sent locusts, and there was a darkness so intense it was felt.
In Revelation 16, which will take place during the Tribulation Period, people are afflicted with loathsome and malignant sores. Seas, rivers, and springs will become blood. There will be intense heat waves and darkness, as well as unclean spirits like frogs. Huge hailstones of 100 pounds will fall from the sky.
However, God is also giving people plenty of warning signs and opportunities to receive him. He is being very patient. This is explained in II Peter 3:6-10, and I Timothy 2:4. God has an escape plan for those who put their faith and trust in Jesus Christ. Some people call it the rapture. Remember, the LEFT BEHIND series by Tim Lahaye? What one calls it is not important. The point is that sometime in the near future all the Christians will escape God's wrath and be transported into his presence with immortal bodies. This event will happen in the "twinkling of an eye." (I Thess 4:13-18 and I Cor. 15:51. Because of God's grace you and I can escape the full wrath of God upon the earth.
The biggest demonstration of God's grace was the cross. God loves you. (John 3:16) God accepts you as you are. (Romans 5:8) You do not have to live by the law or earn your salvation. (Ephesians 2:8-9) Publicly confess Jesus as your Savior. (Romans 10:9-10)