To proclaim or put forth in a sermon: preached the gospel.
To advocate, especially to urge acceptance of or compliance with: preached tolerance and peaceful coexistence.
To deliver (a sermon).
v.
intr.
To deliver a sermon.
To give religious or moral instruction, especially in a tedious manner.
[Middle English prechen, from Old French preechier, from Late Latin praedicāre, from Latin, to proclaim : prae-, pre- + dicāre, to proclaim; see deik- in Indo-European roots.] preach'ing·ly adv.
[preech] 
