When a plant grows, it takes from the soil the nutrients it needs to develop. All crops need those nutrients, they are their own essential constituents. For this reason, the soil must replenish them again and again.
The world population is constantly increasing (today we are about 7 billion people), but the arable land is always the same. Therefore, we need the same land to produce more and more food.
Nutrients, such as granulated urea, fertilize. And fertilization helps the land to recover from the effort made in the previous production cycle and to generate a larger number of crops. These well nurtured crops are better able to withstand harsh weather conditions and produce higher quality food.