Have you ever held a conversation with yourself in your head? Of course you have. How does that conversation happen without making a sound with your mouth or receiving sound waves in your ears? You can do it because God made you with a mind that can entertain such.
In chapter 2 of 1 Corinthians, Paul talks about the Holy Spirit language of Wisdom. He emphasizes that people who have the Holy Spirit hear this kind of language. Accepting Christ as Lord and Savior and thereby receiving the Holy Spirit is like turning on the higher conversational functionality of the mind. Verse 16 is a lift from Isaiah 40:13, but he changes it up. Where Isaiah uses the “Spirit of the Lord,” Paul changes it to “the mind of the Lord”--I think to direct our understanding to a critical aspect of hearing the Holy Spirit.
We have conversations with the Holy Spirit through our thinking mind. Paul said that we who have the Holy Spirit have the mind of Christ. We are then able to think things that are communicated to us by the Holy Spirit. This should not be so surprising; God made our mind and wants to have a conversational relationship with us through it. So, if God (through Paul) says that you have the mind of Christ, when you converse with Him, needing wisdom, shouldn’t you trust that he is putting commensurate thoughts in your mind? So what if you don’t hear the booming voice out of the clouds? You have the mind of Christ for every moment and every thought.