It's precisely because I love Psalm 139 so much that I am irritated with the Prayer Book and the Revised Common Lectionaries. For both lectionaries typically edit out two of the most powerful verses in this psalm, lumping them together with verses which curse the wicked and express hatred for enemies (vv. 18-21 in The Book of Common Prayer Psalter). Here are the excised verses:
Search me out, O God, and know my heart;
try me and know my restless thoughts.
Look well whether there be any wickedness in me
and lead me in the way that is everlasting (vv. 22-23).
It's one thing to edit out verses that call for vengeance and hatred (and I say that having written before about how problematic it is to reject the expression of the full range of human feelings expressed by the Psalms as though they are unacceptable or even un-Christian). But editing out these last verses of Psalm 139 means cutting out one of the most beautiful petitions in the Psalter, and a petition that provides an ideal model for breath prayer. And so it's a real shame that we almost never hear these words in public worship.