The Bible defines knowing God in two ways.
First, Scripture refers to knowing Him in terms of a relationship in which you are certain you are a child of God. You know beyond any doubt that when you die, you're going straight to heaven: “These things I've written to you who believe in the name of the Son of God, that you may know that you have eternal life...” (1 John 5:13).
This word “know” means to know absolutely—like you know how many fingers are on your right hand, how old you are, or what your address is. You should be just as certain that you have eternal life.
The Bible explains clearly how to have that certainty. We must admit that we are sinners who deserve to be forever separated from God. God demands perfection, and even the smallest sin must be punished. The punishment for sin is eternal separation from God: “For the wages of sin is death…” (Rom. 6:23).
We must then recognize that Jesus Christ, the perfect Son of God took that punishment for our sins by dying on a cross in our place: “But God demonstrates His own love toward us, in that while we were still sinners, Christ died for us” (Rom. 5:8). The third day He arose as proof of His victory over sin.
Lastly, we must trust in Christ as our only way to heaven: “But as many as received Him, to them He gave the right to become children of God, to those who believe in His name” (John 1:12).
The moment you trust Christ, you are a child of God eternally and can be certain of heaven. At that point not only do you know God, but you belong to Him forever.
The second way the Bible defines knowing God is in terms of closeness, fellowship, or communion experienced by those who have trusted Christ as their personal Savior. In walking in obedience to Him each day, you experience the closeness of His presence.
For example, utilizing a different word for know in the original language, 1 John 4:7 tells us, “Beloved, let us love one another, for love is of God; and everyone who loves is born of God and knows God.”
In this verse, “know” means to know someone with whom you have spent time, gained experience, and talked. It is the way two close friends know each other. After we trust Christ to save us, God wants us to know Him even better by talking to Him through prayer and listening to Him through Scripture. In the above context, the point is made that the better we know God, the more we learn how to love others the way He loves us.
The invitation to “know God” is one God extends to everyone. He wants us to first know Him by trusting Christ and becoming His child. Then He wants us to know Him better by learning more about Him and walking in close fellowship with Him each day.