“I, even I, am the LORD; and beside me there is no saviour. I have declared, and have saved, and I have shewed, when there was no strange god among you: therefore ye are my witnesses, saith the LORD, that I am God.”
Our Father was talking to the seed of Jacob whose name was later changed to Israel, who of course founded the Twelve Tribes of Israel. Our Father is saying they, the Twelve Tribes, all of them are our Father’s Witnesses.
Witness of what? Witness of His Word. From generation to generation they are to pass down their accounts and God’s Word the Bible to the next and they are to share it with the world. That is their job in this age of flesh.
Our Father never leaves anyone out though. You will notice in verse 7 He says, “Even every one that is called by my name: for I have created him for my glory, I have formed him; yea, I have made him.” Specifically, the Twelve Tribes are the Witnesses of our Father, but God has extended that to “whomsoever will“. Verse 9 continues that point.
Remember, your duty in life is not only to be a good Christian, but ensuring that you are a good example for our Father. As one of His Witnesses, people see your actions in life and it can be a very influencing factor for them.