Why did President Lincoln state, "If McClellan is not using the army, I should like to borrow it"?

Lincoln made this comment on April 9, 1862 expressing his frustration with the commanding General of the Potomac Army George B. McClellan, who was reputable for always being very slow to attack.

a. because the u.s. was the leading with the most technology, economy, etc. also was teamed with other allies witch boosted the economy and materials to improve technology and use it.