What does Psalm 33:15 mean?

The Lord sees not only everyone's outward acts, but also the thoughts and intentions of everyone's heart (Hebrews 4:12–13). Luke 9:46–47 informs us that when the disciples were arguing about who was the greatest, Jesus knew the reasoning of their hearts. As the creator of human beings, the Lord knows what lies in our deepest thoughts and motivations.

Jeremiah 17:9–10 reveals: "The heart is deceitful above all things, and desperately sick; who can understand it? 'I the LORD search the heart and test the mind, to give every man according to his ways, according to the fruit of his deeds.'" Fortunately, the Lord can perform spiritual heart surgery and heal the heart (Psalm 51:10). Acts 16:14 reports that the Lord opened the heart of a woman named Lydia to pay attention to the gospel Paul preached. She became a believer and an ardent follower of Christ. Second Chronicles 16:9 tells us, "For the eyes of the LORD run to and fro throughout the whole earth, to give strong support to those whose heart is blameless toward him."