“But just as it is written, ‘Things that no eye has seen, or ear heard, or mind imagined, are the things God has prepared for those who love him.'”
1 Corinthians 2.9
Paul quotes Isaiah 64.4 to emphasize the wonder of Christ. God is working out his plan. He has revealed it to man. Only those who love him will benefit from it.
“Mind” translates the word for heart, referring to the whole inner person, and often a specific aspect of it. Here, the thoughts of man. Love is the condition of receiving such wonderful things.