There are two points I wish to discuss in this chapter. First, we cannot take our own sins away. Second, are we prepared to accept a call when we are called?
Thy Sin Purged
In verse 5, Isaiah laments that his lips are not clean and that his sins prevent him from being worthy to be in the presence of God. Therefore, in verses 6 & 7, a seraph takes a hot coal and places it on Isaiah's lips thus cleansing him from his sins. The seraph says, "thine iniquity is taken away, and thy sin purged." Similarly, Enos begged for forgiveness and received this reply from God, "thy sins are forgiven thee" (Enos 1:5).
The lesson learned here is that we cannot take away our own sins. No matter what we do and how much we serve, we will still remain sinners. It is only through the Atonement that we can obtain a forgiveness of our sins.
Whom Shall I Send?
In verse 8, Isaiah hears the voice of the Lord saying, "Whom shall I send, and who will go for us?" Isaiah responds, just as the Messiah did, "Here I am; send me." In Abraham 3:27, the same question is posed and the Lord responds in like manner.
What can we learn from it? We can ask ourselves if we are willing to respond in the affirmative when we are asked to serve. If we are worthy, the we will be able to say yes. If we are not worthy, then we must change those things in our lives that will enable us to serve worthily.
We ought to always be prepared to serve when called upon.
A Virgin Shall Conceive
Chapter 17 is very difficult to understand if you do not know the history behind it. I recommend reading an Institute of Religion study manual or a site like gospeldoctrine.com to gain some understanding of the history behind King Ahaz. The gospeldoctrine.com entry for this chapter can be found here.
The most important part of this chapter is when Isaiah prophesies to Ahaz the coming of Christ. He prophesies that Christ will be born of a virgin.