A major function of plants roots is to

Carry nutrients from the soil to the plant

The answer to this is to carry the nutrients to the plants. What it does is the roots are the ones that collect the nutrients from the soil and the dead organisms (plant and animals) and it carries the nutrients from the roots to the stem call the Xylem. After a while the nutrients is carried to the leaves and the sunlight makes the nutrients into food that the plants need and thats how the plant survives.