The major difference between these two documents comes mainly from the fact that Common Sense is a much longer work than the Declaration of Independence is. This means that Paine’s work is able to touch on many more points than the Declaration is.
The Declaration of Independence is a very short document. It touches only briefly on a number of subjects. It is meant to argue that the American colonies have the right to break away from England and to become independent. Paine’s work is meant to accomplish the same thing. The main difference is simply that it is much longer and therefore more detailed.
For example, both documents argue that the system of government under the British was unjust. The Declaration does this largely by talking about the ideas of the consent of the governed and inalienable rights. It says that both of these were denied by the British. By contrast, Paine goes into much more detail. As one example of this, he sets out reasons why the British system fails to provide adequate checks on the king. He simply can go into much more depth than the Declaration can.
Common Sense also serves as much more of a detailed call to action. The Declaration does list supposed abuses by the king. However, Paine’s work goes into great detail about why this particular point in history is a good time to rebel.
There is no real difference in the messages of these two works. The main difference is really that Common Sense is much longer and therefore more detailed than the Declaration.