why did Jesus curse the fig tree?

it seems to be an object lesson.

"The presence of a fruitful fig tree was considered to be a symbol of blessing and prosperity for the nation of Israel. Likewise, the absence or death of a fig tree would symbolize judgment and rejection. Symbolically, the fig tree represented the spiritual deadness of Israel, who while very religious outwardly with all the sacrifices and ceremonies, were spiritually barren because of their sins. By cleansing the Temple and cursing the fig tree, causing it to whither and die, Jesus was pronouncing His coming judgment of Israel and demonstrating His power to carry it out. It also teaches the principle that religious profession and observance are not enough to guarantee salvation, unless there is the fruit of genuine salvation evidenced in the life of the person. James would later echo this truth when he wrote that “faith without works is dead” (James 2:26). The lesson of the fig tree is that we should bear spiritual fruit (Galatians 5:22-23), not just give an appearance of religiosity. God judges fruitlessness, and expects that those who have a relationship with Him will “bear much fruit” (John 15:5-8)."


Source: http://www.gotquestions.org/curse-fig-tree.html#ixzz2nPSoNHqV