Look at my hands and my feet. When he had said this, he showed them his hands and feet. Then he opened their minds so they could understand the Scriptures. You are witnesses of these things. On an earlier occasion, Jesus had appeared to the two disciples who were on their way to Emmaus, a village about seven miles from Jerusalem.
Witness is a translation of the Greek word martyr.
Some of this witnessing to the world requires martyrdom. Through the reunion with Jesus, the disciples' minds were opened to understand about Him as written in the Scriptures. Since they have witnessed that the Scriptures were fulfilled by Jesus, the disciples were now to preach in Jesus' name about repentance and forgiveness of sins to the entire world, with the power from the Holy Spirit as promised by God through Jesus.