The five grains (listed above in section 5:2) have special significance, as they are necessary to produce bread, the most essential food (as well as baked goods and many cooked dishes). Before eating bread, we ritually wash our hands (section 6) and say the Ha-motzi blessing (section 7).
Cooked dishes made from grain, such as orzo or noodles, do not have the same status as bread. Even if one is full after eating them, one does not say Birkat Ha-mazon. Rather, we say Mezonot before eating them and Al Ha-miĥya afterwards.
Baked goods made of the five grains, such as cakes and crackers, have an intermediate status. As long as they are eaten as snacks between meals, we say Mezonot before eating them and Al Ha-miĥya afterwards. However, if one eats them as a meal, they are considered to be bread, so we say Ha-motzi before eating and Birkat Ha-mazon afterwards.