Psalm 14:1 and Psalm 53:1 say that “the fool says in his heart, ‘There is no God.’” Some have understood these words to indicate that atheists are unintelligent. Yet many atheists throughout history have had a very high level of intelligence. In addition, the word "fool" used in the Psalms is one that typically refers to someone who lives in ways morally opposed to God's teachings, not someone who is unintelligent. This saying, therefore, is not related to intelligence but to morality. The most disturbing concern regarding those who say there is no God is that their eternity without faith in God's Son, Jesus Christ, will involve eternal separation from God in hell. This eternal separation reveals the gravity of rejecting God's existence and the saving grace found in Jesus Christ. It serves as a call for believers to share the gospel with love and urgency, inviting others to know the truth of God's existence and His offer of eternal life. True wisdom begins with the fear of the Lord (Proverbs 9:10), submitting to Him and living a life aligned with His will.
These verses are not trying to accuse all atheists of being either unintelligent nor immoral people. The emphasis is that those who claim "there is no God" believe and live in a way that is opposed to God's plan for our lives. Whether an atheist lives immorally or not, the claim is true that to live as if God does not exist stands opposed to the teachings of God's Word.
Then how should Christians treat those who claim there is no God? It is clear that God loves every person, including those who do not believe in Him (John 3:16). He has likewise called us to go and make disciples of all people (Matthew 28:18–20). We must show God's love to those who do not believe in Him and share the message of faith in Jesus Christ, praying for God to open the person's heart to Him.
Further, followers of Christ are called to live a life that is compelling to those who do not believe. Matthew 5:16 teaches, "In the same way, let your light shine before others, so that they may see your good works and give glory to your Father who is in heaven."
Finally, we are called to be prepared to give a reason for the hope within us. First Peter 3:15–16 reads, "but in your hearts honor Christ the Lord as holy, always being prepared to make a defense to anyone who asks you for a reason for the hope that is in you; yet do it with gentleness and respect, having a good conscience, so that, when you are slandered, those who revile your good behavior in Christ may be put to shame." When we both live out our faith and learn all we can about God's Word and its teachings, we can graciously and effectively be used by God to help those who doubt Him and change lives for eternity.