Matthew 28:19-20 says, "Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, and teaching them to obey everything that I have commanded you. And remember, I am with you always, to the end of the age." (New Revised Standard Version)
With these words, Jesus commanded his followers to share the gospel, the good news of his resurrection. This Great Commission is the basis of evangelism in the contemporary church. Many missionaries, Christian organizations, and outreach ministries use these verses in their ministry as Jesus's command for sharing the gospel with their neighbors, both near and far.
However, we should also consider the motivations behind why people share the gospel. As I see it, there are two different motivations, obligation and complete willingness. These two motivations are not polar, someone may be both completely willing and feel obligated to share the gospel. But of these two, to share the gospel completely out of a sense of obligation is more worldly.
The feeling of obligation to share the gospel comes from the Great Commission. People can feel like it is their duty to share the gospel, even if they do not want to themselves. The danger in this motivation is that it stems from ourselves and not the love of Christ. Often, this motivation can rise from guilt or our obligations to do good works for God. Both of these are worldly.
Paul wrote in Philippians 2:3, "Do nothing from self ambition or conceit, but in humility regard others as better then yourselves." Sharing the gospel through a sense of obligation would fit into this first group. When someone shares the gospel based solely on obligations, they do not do so out of God's will, but they try to please God through their works because they believe that God expects it of them. Essentially, their actions are good works done without true faith.
The other motivation is Complete Willingness. This is the more heavenly motivation as this involves true faith. In order to do God's will one must surrender their own will to God. The sharing of the gospel with this motivation is still a work, but it is a work that stems from faith and not for the sake of the work alone.
Overall, while sharing the gospel is a good thing that was commanded by Christ, the motives behind this work are also important. When done solely out of obligation, the work is a selfish deed done to try to please God. But when it is done with surrender to God and the complete willingness to do his will, then the work stems from faith and out of the love of Christ.