Our Lord's command to make disciples of all the nations (Matthew 28:18-20) would have to include any and all atheists in those nations. There is not a single person Christians are not called to evangelize; the good news should be shared with everyone.
Are Christians called to evangelize atheists?
Did the sower of the seed in Jesus' parable only sow on the good ground ready to receive the seed (Matthew 13:3-9)? No, even the hard ground was sown upon (verse 4). When Paul preached in Gentile cities, did he ask all atheists to please leave before he started his sermon? No, he preached for all to hear (Acts 16:6). Did our Lord say, "You will be my witnesses to everyone who already believes in God"? No, He simply said, "You will be my witnesses" (Acts 1:8).
We are responsible to share the gospel with everyone, including atheists; God is responsible for the outcome. We cannot force anyone to believe in Jesus or to convert to Christianity. In witnessing to atheists, our goal is not to argue or philosophize; it is to inform them of Jesus' death, burial, and resurrection. Each person can freely reject the love of Jesus if he or she chooses to do so. The parable of the sower and the seed, mentioned above, illustrates that not every person who hears the gospel will respond positively (Matthew 13:3-9).
Our concern in sharing the gospel with atheists is often that we will be rejected. We tend to fear rejection. Yet God has not given us the spirit of fear (2 Timothy 1:7). We are not ashamed of the gospel, for it is the power of God for everyone who believes (Romans 1:16). Those who do reject us ultimately reject God: "The one who hears you hears me, and the one who rejects you rejects me, and the one who rejects me rejects him who sent me," Jesus said (Luke 10:16). We must be willing to share Christ even in difficult situations, knowing God will use His Word to change lives for eternity. There will be many former atheists in heaven because someone shared the gospel with them and God changed their heart.
What is Christian apologetics and why is it important?
Can the existence of God be proven?
What is truth?
What is Christian tolerance? Should Christians be tolerant of other religious beliefs?
What is the key to evangelizing friends and family without offending them?
Truth about Worldview and Apologetics