Luke 24:44-49 (KJV) And he said unto them, These are the words which I spake unto you, while I was yet with you, that all things must be fulfilled, which were written in the law of Moses, and in the prophets, and in the psalms, concerning me.
Then opened he their understanding, that they might understand the scriptures,
And said unto them, Thus it is written, and thus it behoved Christ to suffer, and to rise from the dead the third day:
And that repentance and remission of sins should be preached in his name among all nations, beginning at Jerusalem.
And ye are witnesses of these things.
And, behold, I send the promise of my Father upon you: but tarry ye in the city of Jerusalem, until ye be endued with power from on high.

This quote is by Ellen White
Desire of ages
Page 805
Now we see

The disciples began to realize the nature and extent of their work. They were to proclaim to the world the wonderful truths which Christ had entrusted to them. The events of His life, His death and resurrection, the prophecies that pointed to these events, the sacredness of the law of God, the mysteries of the plan of salvation, the power of Jesus for the remission of sins,—to all these things they were witnesses, and they were to make them known to the world. They were to proclaim the gospel of peace and salvation through repentance and the power of the Saviour.