Our Thoughts and Ways vs God’s Thoughts and Ways
Isaiah 55:8–9 (ESV) … “For my thoughts are not your thoughts, neither are your ways my ways, declares the Lord. For as the heavens are higher than the earth, so are my ways higher than your ways and my thoughts than your thoughts.”
A striking chiasm characterizes this and the preceding verse. There the prophet spoke of ways and thoughts, here of thoughts and ways. The purpose is to state that God possesses thoughts (i.e. purposes and designs) and ways, and that these are not to be identified with those of man. The emphatic negative before my thoughts and your ways constitutes a full and complete denial of any identity. Not to be overlooked is the chiastic arrangement of the suffixes: MY thoughts, YOUR thoughts: YOUR ways, MY ways. Emphasis is given to the whole by the concluding statement, utterance of the Lord.
In what respect are God’s thoughts and ways not to be identified with those of man? The present verse answers that question. In order the better to understand what we believe to be the correct view it will be well briefly to examine some alternate positions. It has been suggested that man would never think that the wicked could be pardoned, but God thinks differently. The point of difference on this position has to do with what God and man think about salvation. But as a matter of fact the Jews did look for a deliverer to come, and the promises of salvation were actually known to them. A more general statement of this position is that to man salvation would appear impossible, whereas with God it would not be impossible. This interpretation is thus an example of what our Lord uttered in Matthew 19:26. But why should the Jews think that salvation was impossible when God had uttered so many promises concerning it? Again, it has been held that the Jews were prejudiced against the calling of the Gentiles and this promise was intended to correct that prejudice. Surely, however, this is not the natural conclusion that comes to one’s mind as he reads the verse.
There does appear to be a connection between the ways of the wicked, the thoughts of the unrighteous man of verse 7, and the expression thoughts and ways in verse 8. The sinner must forsake his own ways, because his ways are not those of God. Alexander, we think, is correct when he says that this at least affords the formal basis of the true interpretation. But in itself this does not do sufficient justice to the language of the present verse. God’s ways and thoughts, unlike those of the wicked, are righteous; and for that reason the wicked must abandon his own ways and thoughts. God’s mercy and grace are such also as could never have entered the heart of the wicked man apart from special revelation, hence the wicked is to leave his own thoughts. God’s ways and thoughts are sovereignly efficacious, in that they accomplish all that they are designed to accomplish.
Such thoughts, however, in contrast to those of wicked men, are as high above mankind as the heavens above the earth. Emphasis falls upon the concept of height, and the position of the verb at the beginning of each clause is striking. The implication is that just as the heavens are so high above the earth that by human standards their height cannot be measured, so also are God’s ways and thoughts so above those of man that they cannot be grasped by man in their fullness. In other words, the ways and thoughts of God are incomprehensible to man. Even though God reveal them to man, he cannot fully understand them; to him they are incomprehensible. It is for this reason that God’s ways are not to be identified with man’s ways. 
 Young, E. (1972). The Book of Isaiah, Chapters 40–66 (Vol. 3, pp. 382–383). Wm. B. Eerdmans Publishing Co.