For who has known or understood the mind (the counsels and purposes) of the Lord so as to guide and instruct Him and give Him knowledge? But we have the mind of Christ (the Messiah) and do hold the thoughts (feelings and purposes) of His heart. 1 Corinthians 2:16 (AMPC)
This is part of the revelation of our oneness with God in Christ. This means that we share in all that God is and has through union with Christ.
Firstly we are in Christ. 1 Corinthians 1:30 (NKJV) But of Him you are in Christ Jesus, who became for us wisdom from God—and righteousness and sanctification and redemption.
He’s the Vine we are the branches. We live in Him. We move in Him. We have our being in Him.
Secondly Christ is in us. Colossians 1:27 (NKJV) To them God willed to make known what are the riches of the glory of this mystery among the Gentiles: which is Christ in you, the hope of glory. He is our life. He lives in us.
This means we are in union with Christ right from our innermost being. 1 Corinthians 6:17 (NKJV) But he who is joined to the Lord is one spirit [with Him.]
We share in all that Christ is. We have what Christ has. We have His Spirit. We have His Life.
We have the mind of Christ. We have His thoughts, plans, and purposes on the inside of us. The mind of Christ is not in our human mind or brain for Scripture tells us to renew our minds. Romans 12:2. The mind of Christ is in our heart or spirit.
Renewing our mind is actually getting our human mind or brain to think in line with and yield to the mind of Christ in our heart.
The Spirit of Christ is joined with our spirit so He communicates all the thoughts, plans, and purposes of God to us in our heart or spirit. Romans 8:16 (NKJV) The Spirit Himself bears witness with our spirit that we are children of God,
The mind of Christ or the mind of God is right in our hearts or spirit. This means everything God has planned and purposed for us is right in our hearts or spirit. Therefore all we need to do in order to find out what God thinks or says about anything is to listen to our heart or spirit.
Now we can understand Proverbs 20:27 (NKJV) The spirit of a man [is] the lamp of the LORD, Searching all the inner depths of his heart.
God instructs and leads us from our spirit because that’s where His Spirit is and that’s where He connects and communicates with us. This is what it means to have the mind of Christ.