The theme of The Shawshank Redemption, as blatantly mentioned in the scene above, is hope. Andy Dufresne is a wrongly accused convict who was sent to a prison where most people would lose all hope. Andy didn't and knew he had to keep his feeling of self-worth to make it in Shawshank. He was one of the only ones who thought hope could be a helpful thing, and in the end he turned out being right.
This theme is mostly reinforced in the scene by use of line, space and rhythm. There isn't much character movement, but there is a moment when the audience can almost share what Red and Andy are feeling towards each other because of their eye contact. When Andy says "Like Brooks did?" the use of virtual lines between he and Red's eyes gives us that sense of feeling between them. The space used is flat and quite limited. All that you are able to see is the characters at the lunch table and some inmates behind them. It's limited to the space of the inside of the cafeteria. The scene shows all of the friends chatting at the table, but once Andy starts getting deep about himself feeling music inside of him the camera uses both zoom and panning (complex shot) to focus in on Andy. This creates a great tension which is released by Red saying how he used to play the harmonica. Tension is felt again in the end of the scene between Andy and Red when Andy proved his point about Brooks losing his hope. There is contrast and affinity seen in the use of lines. The virtual lines between Red and Andy are very intense and deep feeling, while the lines used when Andy is talking to everybody at the table in general feel much more loose and relaxed (though Andy is still talking very thoughtfully.)