“He has told you, ‘O man, what is good, and what does the Lord require of you but to do justice, to love mercy, and to walk in secrecy with the Lord your God’” (Micah 6).
“Walking in secrecy” means something that is secret, that is not visible. Something that is visible is called “revealed,” meaning actions that anyone can see what his friend is doing, but not what his friend is thinking. Even when his friend tells him his thoughts, it is still not certain that this is his real thought.
For example, a person who has made a fortune and then donated it to a religious institution and says he wants to give them this large sum provided they advertise it in the papers. He says that it is worthwhile for him to donate the large sum in order to get the publicity and great respect.
However, even if he says explicitly that his intention is respect, it can be otherwise. That is, he might want to do this so as not to be respected for doing a righteous deed, giving such a large sum although he is not that wealthy, and still because the commandment to support students of Torah is important in his eyes, he donates the money. But in order for people not to say that he is working for the sake of the Creator and respect him for doing a righteous deed, he says that his intention is respect. Therefore, he will not be respected. It follows that a thought cannot be revealed. Rather, something that is revealed is only actions. For this reason, the verse says, “walk in secrecy,” meaning the intention, so it will be “with the Lord your God,” meaning that he should see that the intention is for the sake of the Creator.