Omniscient means all-knowing. From the Latin omni (all) scientia (knowledge).
Some people may argue that if God knows everything then He cannot know what it is like to not know everything and so He cannot, in fact, know everything. This and other similar arguments assume that God’s omniscience refers to His perceiving and experiencing every possible thing.
God’s omniscience is not in His perception or experience of everything possible, but is His conception of everything that is true. God doesn’t have to know every choice that you will make in order to know the consequence of every choice that you could make. God can say, “if you eat from that tree, you will die,” without actually predetermining whether you will eat from the tree or not.
To put this simply, God’s omniscience means that God knows all truth.
And don’t think that because God knows all possible events that could happen that He necessarily must cause any of them to happen. We should instead consider that God knows all possible events that could happen and is happy to let any of them happen. Just because He knows that something could happen does not mean that He actually causes it to happen.
The idea that God knows all things - past, present, and future - and thus causes all things, relies on our concept of time. And remember that God is not burdened by our sense of time because He is eternal.
God knows how the world works, and He is not surprised by the way things turn out.
God knows our limitations. He knows that no person would be born perfect, unless He Himself came to be that person.
God knows our hearts. That humans will pursue things that will lead to the destruction of the world.
God knows our minds. That we will try to know Him, and that some of us will deny Him.
God knows His plan. He knows when to intervene in the world to bring about His will, and when to let things play out. Such as the way He “stood back” and allowed Abraham to have a child with Sarah’s slave, but then He intervened and wiped out Sodom and Gomorrah.
I would say that God does not do things specifically to control every possible outcome in every possible situation, but He does do things to work out His plan for His creation. If something happens that has no effect on the ultimate outcome of His plan, He lets it happen - like Jonah trying to run away from Him. But if anything happens that would throw His plan off, He intervenes - like sending a fish to swallow Jonah and take him to Nineveh. Jonah could have obeyed God, and then God would not have to intervene. But Jonah did not obey Him, and Jonah’s mission was important to God, so God intervened.
And to put things in the eternal perspective of God, think about this. He has a plan for Adam and Eve (and their children) to be His image bearers, and to have dominion over the earth. He “stood back” and allowed Adam and Eve to sin, which seems like it would have ruined His plan. But then He intervened by sending Jesus to die for our sins, and He will one day create a new heaven and a new earth in order to fulfill His plan. So, what we might think of as “bad,” God can actually turn into good. He just does it in His own way, in His own time.
God knows everything because He created everything, and He is in everything. He also has a plan for everything, and He uses all things for His good.
To us it is hard to understand how anyone could know everything. That is how limited our understanding is - we can’t even comprehend what it would be like to know everything. But God is infinite, remember. God does not have limitations like we do.
Remember the fishbowl analogy I used a few articles ago? It’s as if we live in a fishbowl in God’s kitchen, and we don’t even know most of what there is to know about the fishbowl. But God knows everything about the fishbowl, and everything in the fishbowl, and everything outside of the fishbowl. He doesn’t have to predetermine every path that each fish will swim along in order to know everything about each fish, and everything about how each fish will effect all the other life in the fishbowl.
He doesn’t have to force each fish to swim an exact path, but He might stick His finger in the water every now and then to redirect a fish to go where He wants it to for a specific reason. The fish could turn around, or bite His finger, or go left when He wants it to go right - and God always knows that any of these outcomes are possible at any moment. The fish does not lose free will at any time, but those fish who are attentive to God will try to follow His finger whenever they see it - and following Him is absolutely done out of their own free will.
Psalm 147:5 (NASB95) Great is our Lord and abundant in strength; His understanding is infinite.
Ezekiel 11:5 (NLT) Then the Spirit of the LORD came upon me, and he told me to say, “This is what the LORD says to the people of Israel: I know what you are saying, for I know every thought that comes into your minds.
Acts 15:16-18 (NLT) ‘Afterward I will return and restore the fallen house of David. I will rebuild its ruins and restore it, so that the rest of humanity might seek the LORD, including the Gentiles— all those I have called to be mine. The LORD has spoken— he who made these things known so long ago.’
Romans 11:33 (NLT) Oh, how great are God’s riches and wisdom and knowledge! How impossible it is for us to understand his decisions and his ways!
Hebrews 4:13 (NLT) Nothing in all creation is hidden from God. Everything is naked and exposed before his eyes, and he is the one to whom we are accountable.
1 John 3:20 (NLT) Our actions will show that we belong to the truth, so we will be confident when we stand before God. Even if we feel guilty, God is greater than our feelings, and he knows everything.