Final answer:
Missions in the sense of Christian evangelism are most clearly represented in the New Testament, notably in Jesus's Great Commission in Matthew 28:19-20 and Paul's missionary journeys in the Acts of the Apostles.
Step-by-step explanation:
The concept of missions or missionary work is mentioned several times in the Christian Bible. While the Old Testament includes instances of God sending prophets to call the people of Israel back to faithfulness, the idea of missions as it is understood in the context of Christian evangelism is more clearly articulated in the New Testament.
Two notable instances include Jesus's Great Commission to his disciples found in Matthew 28:19-20, where Jesus commands his followers to 'go and make disciples of all nations,' and the extensive missionary journeys undertaken by the Apostle Paul, as detailed in the Acts of the Apostles.
Early Christianity was marked by missionary activities, as shown by the efforts of individuals like Paul and other followers to spread the Christian faith across the Roman Empire and beyond.