The word speaks mostly to Believers as a body, so Christ says you shall be "witnesses", plural. Of course, in practice there is both the collective witness and the individual witness.
But, what does it mean to be a witness to Jesus? Firstly, it means that the activities of a Body of Believers and the individual Believer are done in the name of Jesus.
However, the way of life of a Believer who truly is a new creation (1 Corinthians 5'17) witnesses to Him every day.
There are some very powerful and encouraging scriptures about that.
"... we are to God the fragrance of Christ among those who are being saved and among those who are perishing," 2 Corinthians 2'14-15.
“You are the salt of the earth ..." Matthew 5'13.
And there is no striving involved:
“You are the light of the world. A city that is set on a hill cannot be hidden.
Nor do they light a lamp and put it under a basket, but on a lampstand, and it gives light to all who are in the house.
Let your light so shine before men, that they may see your good works and glorify your Father in heaven," Matthew 5'14-16.
It's all a matter of letting His aroma emanate, letting His light shine. Jesus said: "you shall be witnesses". It's a state of spiritual being. Because:
"... it is the God who commanded light to shine out of darkness,
who has shone in our hearts
to give the light of the knowledge of the glory of God
in the face of Jesus Christ.
But we have this treasure in earthen vessels, that the excellence of the power may be of God and not of us," 2 Corinthians 4'6-7.
That's truly awesome!
"For you were once darkness, but now you are light in the Lord. Walk as children of light," Ephesians 5'8.
All these things contribute to witnessing powerfully, even unconsciously.
Jesus has commissioned His Followers, who have the glorious treasure in their hearts, with these amazing words:
"As the Father has sent Me, I also send you," John 20'21.
Jesus, as the Anointed One, sends His "earthen vessels" into the world in the grace, love and power of the same Holy Spirit as He did. Like these did:
"And they went out and preached everywhere, the Lord working with them and confirming the word through the accompanying signs, Mark 16'20.
It has been said that signs only accompany those who lead but do not accompany "ordinary" Believers. Not so! The Lord said:
"Most assuredly, I say to you,
he who believes in Me,
the works that I do he will do also;
and greater works than these he will do,
because I go to My Father,"