If you have a cell that contains a large sentence that is not easy to read without resizing the cell, you can use the justify function to split the large sentence into other cells without the need for copy and paste.
Highlight the cell with the sentence you want to split (NOTE this requires blank cells to be beneath)
Excel 2007 click Home -> Editing -> Fill -> Justify
Excel 2000 – 2003 click Edit -> Fill -> Justify.
This will result in the text from the cell you selected being split into the cells beneath.