In this passage we see, perhaps, a hint of the triune nature of the Godhead. It is as if God the Father is inquiring of God the Son and God the Spirit as to whom other than one of them would be an effective representative for them. Isaiah, in his freshly forgiven and purified state (vv. 6-7), offers to accept the commission and represent the Father, the Son, and the Spirit. A similar call is issued to each of us today.

Elsewhere in Scripture we are told more plainly of the fullness of our call to represent God the Father: "Ye are my witnesses, saith the LORD, and my servant whom I have chosen: that ye may know and believe me, and understand that I am he: before me there was no God formed, neither shall there be after me. I, even I, am the LORD; and beside me there is no saviour" (Isaiah 43:10-11).

Likewise, God the Son called us to be "witnesses unto me both in Jerusalem, and in all Judaea, and in Samaria, and unto the uttermost part of the earth" (Acts 1:8).

Conversely, we are not called to be witnesses of the Holy Spirit; rather, we are to be co-witnesses with Him of Jesus Christ. "But when the Comforter is come, whom I will send unto you from the Father, even the Spirit of truth, which proceedeth from the Father, he shall testify of me: And ye also shall bear witness, because ye have been with me from the beginning" (John 15:26-27). "When he, the Spirit of truth, is come, he will guide you into all truth: for he shall not speak of himself; but whatsoever he shall hear, that shall he speak: and he will shew you things to come. He shall glorify me: for he shall receive of mine, and shall show it unto you" (16:13-14).

What a privilege! What a message! What a Partner! JDM

http://www.icr.org/article/6571/