Isa 55:9 “For as the heavens are higher than the earth, So are My ways higher than your ways, And My thoughts than your thoughts.

This verse is used as a catch-all verse to dismiss arguments. If anything is said of God that a Christian finds offensive and does not want to believe, then this verse is used to dismiss the idea without examination. But this verse is not used in Isaiah in some sort of blanket distancing God from human kind. Instead, this verse specifically means that God shows mercy to the repentant rather than exact vengeance. This is not some sort of absolute distinction meaning no person could conceivably act like God, but instead, it means that humans tend to be vengeful whereas God shows mercy even in extreme cases.

Examining the context:

Isa 55:3 Incline your ear, and come to Me. Hear, and your soul shall live; And I will make an everlasting covenant with you— The sure mercies of David.
Isa 55:4 Indeed I have given him as a witness to the people, A leader and commander for the people.
Isa 55:5 Surely you shall call a nation you do not know, And nations who do not know you shall run to you, Because of the LORD your God, And the Holy One of Israel; For He has glorified you.”
Isa 55:6 Seek the LORD while He may be found, Call upon Him while He is near.

The first set of verses in this chapter are dedicated to wooing Israel. God calls Israel to repentance. If they repent, God will make a covenant with them. They will be a strong nation whom can command other nations to action. God will be their God and they will be God’s people.

But as of now, there is a problem. The people are wicked, so wicked that they risk being punished in spite of any repentance. It is this that God tries to dispel:

Isa 55:7 Let the wicked forsake his way, And the unrighteous man his thoughts; Let him return to the LORD, And He will have mercy on him; And to our God, For He will abundantly pardon.
Isa 55:8 “For My thoughts are not your thoughts, Nor are your ways My ways,” says the LORD.
Isa 55:9 “For as the heavens are higher than the earth, So are My ways higher than your ways, And My thoughts than your thoughts.

God wants the wicked to repent. It is them to whom God says “My thoughts are not your thoughts.” It is that person whom God will pardon, because “God’s ways are not his ways.” Normal people, especially the wicked audience of this chapter, would not pardon as God does. But God promises blessings for the wicked if they repent.

God then proceeds to detail His promise of blessings:

Isa 55:10 “For as the rain comes down, and the snow from heaven, And do not return there, But water the earth, And make it bring forth and bud, That it may give seed to the sower And bread to the eater,
Isa 55:11 So shall My word be that goes forth from My mouth; It shall not return to Me void, But it shall accomplish what I please, And it shall prosper in the thing for which I sent it.

God is not lying when He promises blessings to the repentant. Just as the rain creates green grass rather than just returning to the sky, God will create prosperity without His work returning fruitless. This is the context of God’s word not returning to Him void.

God then paints a picture of the paradise He is promising:

Isa 55:12 “For you shall go out with joy, And be led out with peace; The mountains and the hills Shall break forth into singing before you, And all the trees of the field shall clap their hands.
Isa 55:13 Instead of the thorn shall come up the cypress tree, And instead of the brier shall come up the myrtle tree; And it shall be to the LORD for a name, For an everlasting sign that shall not be cut off.”