Jesus was giving his final instructions to the apostles and mentioned what he had taught them and that it had been written in the Old Testament (Lk 24:48). He then said, "'You are witnesses of these things'" (:48). It means that they had experienced the prophecys coming true. In court a witness is someone who has observed something taking place. Peter repeatedly stated "we are witnesses of these things and so is the Holy Spirit" (Ac 5:32) and "we are witnesses of all the things He did both in the land of the Jews and in Jerusalem" (10:39). More importantly John said that Jesus "dwelt among us, and we saw His glory as of the only begotten from the Father" (Jn 1:14). Peter said "we ourselves heard this utterance made from heaven when we were with Him on the holy mountain" (2Pe 1:18). Then what does it mean when Jesus said "'you shall be My witnesses'" (Ac 1:8) since they were, in effect, already witnesses? In this case the phrase follows "'you will receive power when the Holy Spirit has come upon you'" (:8). It means you will have supernatural power to be future witnesses in a way you would not have had on your own. "We have this treasure in jars of clay to show that this all-surpassing power is from God and not from us" (1Co 4:7). Inherent in this is that there is a responsibility to witness, and motivation is provided by the Spirit to accomplish it. "God anointed Him [Jesus] with the Holy Spirit and with power . . . [so that] He went about doing good and healing all" (10:38). It's easy to mistakenly conclude when you hear the term "great commission" that now I have to do it myself. However, Jesus made it clear saying, "'I, if I am lifted up from the earth, will draw all men to Myself'" (Jn 12:32). Jesus said, "'I sent you to reap'" (4:38). "'Beseech the Lord of the harvest to send out laborers into His harvest'" (Lk 10:2).