The Church actually uses both the Hebrew and the Greek versions of the Old Testament books. Which one is used depends upon a variety of circumstances but the general rule of thumb is to use the oldest and most intact version. We need to remember that for books that were originally written in Hebrew that the Greek versions are translations and not originals. Sometimes ideas, imagery, or word play can lose something when translated into another language. However, if a Hebrew word can have several meanings and a more specific Greek word is used in the LXX then usually the LXX translation would be used (unless tradition unanimously argues otherwise). And, of course, anytime the New Testament uses a particular version then we presume that the use of that version was inspired.
