In Isaiah 55:8 we find the phrase "my thoughts are not your thoughts."
"My thoughts are nothing like your thoughts," says the Lord. "And my ways are far beyond anything you could imagine. (New Living Translation)
"For My thoughts are not your thoughts, Nor are your ways My ways," says the Lord. (New King James Version)
"My thoughts," says the Lord, "are not like yours, and my ways are different from yours. (Good News Translation)
Our Bible Commentary says this about Isaiah 55:
Chapter 55 begins with the analogy cited by Jesus in the New Testament of the water of life—the Holy Spirit (see John 4:10-14; John 7:37-38; Revelation 21:6; Revelation 22:1, Revelation 17). This ties back to earlier references in Isaiah, such as Isaiah 12:3 and Isaiah 44:3. We are told to buy even though we have no money. It is a totally free gift—albeit a gift with conditions. God requires only true repentance accompanied by faith and then baptism (see Acts 2:38; Hebrews 11:6). Of course, what many do not understand is that repentance is more than just being sorry for past sins. It also involves a lifelong commitment to obeying God.
"Wine and milk [in Isaiah 55:1] are symbols of complete satisfaction ( Isaiah 55:2). Not only does God's salvation supply what is necessary for life, but it also provides what brings joy" (Nelson Study Bible, note on verse 1). As Jesus said, "I have come that they may have life, and that they may have it more abundantly" (John 10:10)—meaning now and on into eternity beyond. "Abundance" is directly mentioned in verse 2 of Isaiah 55. Notice also that the invitation to "eat" and "delight" in abundance can be likened to a banquet. Jesus gave parables that picture salvation as partaking of a banquet (see Matthew 8:11; Luke 14:15-24). Isaiah 55:2 mentions the bread analogy used by Jesus as well (see John 6:48-58).
Verse 3 of Isaiah 55 mentions the "sure mercies of David" (Isaiah 55;3). Paul explained in his speech at Antioch of Pisidia in Acts 13:34 that this referred to Jesus being raised from the dead, and he goes on to cite Psalm 16 of David, which is full of many promises of future inheritance, blessings and pleasures. These "sure mercies" are also described here as an "everlasting covenant" that God is willing to make with all who "thirst" and come to God. And David was a witness of these promises (Isaiah 55:4). Indeed, there may also be a reference here to the Davidic covenant itself—wherein God promised David an eternal offspring, throne and kingdom. This, of course, is ultimately fulfilled in Christ—who was destined to inherit the throne of David. Yet this promise is for us as well—since Jesus said that His followers would share His throne with Him (see Revelation 3:21; compare Romans 8:17).
Isaiah 55 goes on to say that even the wicked may seek and find God if they forsake their wrong way and "return" to Him—the Old Testament term for repent. God says He will have mercy, immediately followed by a statement that His thoughts and ways are higher than our thoughts and ways. In its note on Isaiah 55:6-7, The Bible Reader's Companion states: "It is in the free pardon that God offers the wicked that the sharpest difference between God's thoughts and our thoughts are seen. We feel anger and outrage and call for revenge. God feels compassion and love and extends mercy. Thus God's word is gentle and life-giving; in Isaiah's analogy, like the gentle rain that waters the earth and causes life to spring up. What a warm and wonderful view of God (Isaiah 55:10)."
The chapter ends with God's people leaving their exile. Again, this should be understood as having multiple applications: the Jews leaving Babylonian captivity; Israel and Judah leaving their end-time captivity; spiritual Israel receiving its deliverance through Christ today; the ultimate deliverance of spiritual Israel in its glorification at Christ's return; the spiritual deliverance of physical Israel and all mankind when they are joined to spiritual Israel through Christ; and finally their ultimate deliverance when they are glorified as well. Commentators explain this chapter as being the last one addressed to the people in captivity. The remaining chapters of Isaiah are claimed by many to be addressed to a post-exilic audience.