You are witnesses of these things and preached in Jesus name to all nations, beginning at Jerusalem

 Luke 24:44-53

He said to them, “This is what I told you while I was still with you: Everything must be fulfilled that is written about me in the Law of Moses, the Prophets and the Psalms.”

Then he opened their minds so they could understand the Scriptures. He told them, “This is what is written: The Messiah will suffer and rise from the dead on the third day, and repentance for the forgiveness of sins will be preached in his name to all nations, beginning at Jerusalem. You are witnesses of these things. I am going to send you what my Father has promised; but stay in the city until you have been clothed with power from on high.”

When he had led them out to the vicinity of Bethany, he lifted up his hands and blessed them. While he was blessing them, he left them and was taken up into heaven. Then they worshiped him and returned to Jerusalem with great joy. And they stayed continually at the temple, praising God.

Why?
Jesus showed up before the disciples and sent them the mission of preaching the gospel. All of the disciples are the witness of Jesus. And a new mission is preached in Jesus' name to all nations, beginning at Jerusalem.

Before preaching the gospel they need to wait until they have been clothed with power from on high, the Holy Spirit.

Jesus opened their minds so they could understand the Scriptures. I need the Lord to open my mind so that I can understand the Scriptures and tell others in my life.

How?

Preaching the gospel needs the power that comes from the Holy Spirit. May the Lord open my mind to understand the Scriptures and tell others.