Why the image of a fiery serpent?

The speaker at the fireside last night mentioned the fiery serpent Moses was told to lift up among the people. If they would look at the image of the serpent they would be healed. It has always been confusing to me and many others including the speaker why the Lord chose the image of a serpent which represents Satan.

Now the Lords ways are not our ways, his thoughts are not our thoughts and the speaker gave his opinion and I have mine which is a little different. 

This is in no way scripture but the speaker said he felt good about his thoughts so he shared them with us. He said that when Jesus would come he would take upon him our individual sins and in so doing he descended into the very depths of hell in order to save us. He descended below Satan therefore, which caused him the only begotten, the Son of God to bleed from every pore so great was the pain. His having descended to that depth for us, is therefore, the reason for the image of the serpent, or of Satan. This does feel right to me and I agree with it but I feel like there is more to it.  

I think that they needed to look at the image of the serpent because following Satan was what got them into trouble to start with.  I think that they needed to look at their individual sins, and make that choice to accept Christ and give up their sins, because we are not saved ‘in’ our sin. Therefore the people came to Moses and said, “‘We have sinned for we have spoken against the Lord, and against thee.’” (Numbers 21:7)  And as many as looked at the serpent image and repented lived, but for those who would not acknowledge the serpent or their sin died. Christ atonement makes it easy for us to repent and change. Without him it would be impossible, but looking at our sin is not easy, easy. It is ‘easier’ but not easy. This is why it is so important to clean the slate daily, but still we justify and procrastinate.