For thou shalt be his witness unto all men of what thou hast seen and heard. (Acts 22:15)
Paul was chosen to see and hear the Lord speaking to him out of heaven. This divine election was a high privilege for himself; but it was not intended to end with him; it was meant to have an influence upon others, yea, upon all men. It is to Paul that Europe owes the gospel at this hour.
It is ours in our measure to be witnesses of that which the Lord has revealed to us, and it is at our peril that we hide the precious revelation. First, we must see and hear, or we shall have nothing to tell; but when we have done so, we must be eager to bear our testimony. It must be personal: “Thou shalt be.” It must be for Christ: “Thou shalt be his witness.” It must be constant and all absorbing; we are to be this above all other things and to the exclusion of many other matters. Our witness must not be to a select few who will cheerfully receive us but to “all men” — to all whom we can reach, young or old, rich or poor, good or bad. We must never be silent like those who are possessed by a dumb spirit; for the text before us is a command, and a promise, and we must not miss it — “Thou shalt be his witness.” “Ye are my witnesses, saith the Lord.”
A Constant Witness Charles Spurgeon