At the end of Matthew’s Gospel we see the final instructions given by Christ to His Disciples:
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. – Matthew 28:19 (ESV)
This command is pretty straightforward if read at face value with its plain meaning. They were to go and preach the Gospel to all people. But there have been questions regarding this passage and whether or not it would apply to all Christians or only to the Apostles themselves.
Since the beginning of the church, this passage has been understood to apply to all believers as a call for evangelism. But how can we know that is the case? The passage itself gives us that answer.
Teaching them to observe all that I have commanded you – Matthew 28:20a (ESV)
The word for observe is the word tēreō and carries the sense of fulfillment. In other words, the disciples were to evangelize and charge others with fulfilling the commands of Christ, including the Great Commission.