According to Revelation 3:14, God already has a "faithful & true witness" - he doesn't need any more!
However, the scriptures instructed Christians who they were to witness for:
Matthew 10:18 - ".....for my sake, for a witness to them and the nations.
Mark 13:9 - "......before governors and kings for my sake, for a witness to them."
Luke 24: 47,48 - "....and on the basis of his [Jesus'] name....You are to be witnesses....."
John 1:15 - "John bore witness about him..." [JESUS]
John 5:37 - "the Father who sent me has himself borne witness about me."
John 8:18 - "the Father who sent me bears witness about me."
John 15:26,27 - "the spirit will bear witness about me; and YOU in turn, are to bear witness."
Acts 1:8 - "You [11 faithful apostles] will be witnesses of me...."
Acts 4:17,18 - ...upon the basis of this (Jesus') name .... upon the basis of the name of Jesus.
Acts 10:39 - "And we are witnesses of all the things he [Jesus] did..."
Acts 10:43 - "To him [Jesus] all the prophets bear witness....."
Acts 13:31 - "who are now his (Jesus') witnesses to the people.
Acts 22:15 - "because you are to be a witness for him [Jesus] to all men......"
Acts 22:20 - "......the blood of Stephen your [Jesus'] witness was being spilled..."
Acts 23:11 - "..... a thorough witness on the things about me in Jerusalem..."
Acts 26:16 -"I [Jesus]..choose you as an attendant and a witness respecting me"
Romans 8:16 - "The spirit itself bears witness with our spirit..."
1 Corinthians 1:6 - "even as the witness about the Christ..........."
1 Timothy. 2:6 - "......what is to be witnessed to at its own particular times."
2 Timothy 1:8 - "............of the witness about our Lord.. [Christ]"
1 John 5:9 - "the witness God gives...the fact that he has borne witness concerning his Son."
Revelation 1:9 - "....for speaking about God and bearing witness to Jesus."
Revelation 12:17 - ".......and have the work of bearing witness to Jesus."
Revelation 17:6 - "........and with the blood of the witnesses of Jesus."
Revelation 19:10 -".....the work of witnessing to Jesus.... bearing witness to Jesus."
Revelation 20:4 - "............ for the witness they bore to Jesus."
For whose name were Christians to witness? (see 29 scriptures above)
For whose name would Christians be hated? (Matt. 10:22)
By whose name were people healed? (Acts 3:6; Acts 4:10)
By whose name were demons expelled? (Luke 10:17; Acts 16:18)
By whose name would people receive Holy Spirit? (John 14:26)
In whose name would people pray to God? (John 15:16)
By whose name would people be named? (Isa. 62:2; Acts 11:26)
By whose name would people be reconciled to God? (Rom. 5:10; 2 Cor. 5:18)
By whose name would people be forgiven their sins? (Matt. 26:28; Acts 2:38; Eph. 1:7)
In whose name would people be judged? (John 5:27)
By whose name would people be resurrected (John 5:28)
In whose name would people be baptized? (Acts 2:38, 8:16, 10:48, 19:5, 22:16)
In whose name were people to put faith? (John 2:23)
In whose name was Saul/Paul commissioned to preach? (Acts 9:14-16)
For whose name would Christians be reproached? (1 Peter 4:14)
In whose name were Christians to gather together? (Matt. 18:20)
For whose name would Christians make sacrifices? (Matt. 19:29)
For whose name would Christians be persecuted and killed? (Luke 21:12,16,17)
In whose name will every knee in heaven and on earth bend? (Philippians 2:10)
In whose name would people be declared righteous? (1 Cor. 6:11)
By means of whose name would Christians offer a sacrifice of praise? (Hebrews 13:15)
The names 'Jehovah' or 'God' are notable by their absence.
