Isaiah is a long book. It's a long book because Isaiah was a faithful, consistent, and diligent prophet. For Zion's sake he did not keep silent. For Jerusalem's sake he did not keep quiet. For the sake of the church this prophet persevered in preaching and in prayer. Our shepherds of today need to do the same. I for one am thankful to be married to a man who strives to persevere - even against the unbelievable odds that daily bombard him.
Verses 6-7 tell us a little bit about the duties of those watchmen whom God has appointed to keep an eye out on and for our souls.
1) Notice that they have been appointed. "I have appointed watchmen." True watchmen don't take this office upon themselves, it is placed upon them. Here is an inference to the importance of ordination to office. Scripture speaks not only of an internal call ("If a man desires the office of elder it is a good thing" - 1 Tim 3:1)) but also of the external call ("you...appoint elders in every city," - Titus1:5, "with the laying on of hands by the presbytery" -1 Tim 4:14)
2) Notice that it is no cushy, one hour a week job. "All day and night they will never keep silent." Again, I'm married to a watchman and I see much of the behind the scenes. I see the 60, 70 and sometimes 80 hour work weeks that sometimes arise. The faithfully executed office of watchman is 24/7.
3) Notice that it is a self-sacrificing position. "Take no rest for yourselves." Anyone who desires to be a watchman for what it will afford him has missed the picture and purpose of the office. A watchman puts his head on the chopping block for others. Just as Christ, the suffering and sacrificing Servant did for us. It is not a self-serving position it is a selflessly serving position.
And what exactly is this duty that they are to take no rest from? They are to not keep silent regarding the proclamation of God's truth. They are to warn us of the wolves that lie without and within and they are to point us to Christ - the Great Shepherd. And, they are to always be about this business, lest we be carried away by sin, self, and Satan.
"Ministers must do their duty as watchman. They must take all opportunity to give warning to sinners, in season and out of season. They must never betray the cause of Christ by a treacherous or cowardly silence. They must never hold their peace at the throne of grace, but must pray, and not faint."
May God grant His church's watchmen that will not keep silent, nor be quiet until her righteousness goes forth like brightness.