When I took office 3 years ago, my Administration was left an annual deficit of $1.3 trillion, or 9.2 percent of GDP, and a projected 10-year deficit of more than $8 trillion. . . . Together with the deficit reduction I signed into law this past year, this [new] Budget will cut the deficit by $4 trillion. —President Barack Obama, 2012 Budget Message of the President

What is the purpose of the president’s statement?

to show how changes in fiscal policy can affect the economy
to show the size of the deficit relative to GDP
to show how large the national debt was when he took office
to show how he plans to reduce the national debt

This answer can be explained by two things. The first one, the way that the President portrays the way that the economy used to be before he was in office, with a deficit of 1.3 trillion a year and a total of 8 trillion in 10 years, versus the way that his new measures will reduce such deficit to about half of the presuposed deficit for the 10-year period. So he compares what was left for him with what is actually happen after his measures take effect. The second is the actual numerical data that he gives, from the past and the present, and even what is expected for the future. This numerical data alone shows that economical measures, any measures regarding fiscal policy, will have an effect on the economy, either positive or negative.