What are we? What are our lives? ... What can we say before You? (Siddur).
One way to read this prayer is to see the last phrase as an answer to the series of questions posed earlier. Read it: "What are we, and what are our lives and traits? Only that which we say before God." In other words, I can only know that much about myself which I have the courage to reveal to God. That which I cannot own up to, that which I keep so concealed that I cannot verbalize when I communicate with God, remains alien to me.
The Rabbi of Kotzk interpreted the verse, There shall not be a foreign god among you (Psalms 81:10), to mean, "Do not let God be foreign to you." To the degree that we alienate ourselves from God, we also alienate ourselves from ourselves.
Tachanun, the practice of daily soul-searching and teshuvah, is more than a ritual. By disclosing ourselves before God, we become aware of ourselves. While tachanun does contain prescribed prayers of confession, it is highly commendable that following them, we enter into a spontaneous conversation with God, telling Him all our innermost thoughts. In this way, we remove the barriers of denial and repression that both cause us to disown part of ourselves and put our correctable character defects out of reach.