The commentary in the JSB notes that Isaiah chs. 1-5 commonly call for Israel to repent. In Isaiah 6:9-13 the Lord commands Isaiah to tell the people that they will not repent until it is too late. The remainder of Isaiah’s prophecy to Israel prior to the Babylonian exile contains no more calls to repentance. This could signify that the vision in chapter 6 is not Isaiah’s initial call to prophecy; rather, it may be the turning point at which he is no longer to prophecy repentance.