Righteous means to be right.
The unrighteousness of man is spoken of in scriptures like Isaiah 64: 6. & Psalm 51:5 Romans 3: 9-18 to name but a few. As the above scriptures testify man is unrighteous by nature and has a tendency towards sin. That is why Isaiah 55:8 is the truth concerning man, by default man cannot have the same thoughts and ways as God. God is holy, righteous and good. Man is sinful, unrighteous and corrupt. So there is no way man's ways and thoughts are going to be like God's because they are exact opposites in nature.
To be righteous simple means to be right. To be righteous before God means to be in right standing before him. It means that God is able to look into your heart and see nothing but divine glory and light. This righteousness is a free gift of God's grace in Christ. See Romans 3:19-23 & 5:17. When a man receives the free gift of God's grace in Christ, by faith, he is declared the righteousness of God in Christ. 2 Corinthians 5:21. The person who has had this experiences is now able to know God's ways and God's thoughts because he shares the same divine nature.
Blessings,
Tony