Why is it important for the cell membrane to allow materials to enter and leave the cell

Cell membrane needs to allow and exit the materials that enter the cell because the cell needs nutrients and these nutrients are converted into molecules that aid in many cellular activities like repair, divide and form structures and biomolecules.

Also to excrete wastes and other harmful materials for the cell.

This continues because the cell wants to attain homeostasis.

Homeostasis is the state where the internal and external part of the body maintains and establishes balance and equilibrium. This is achieved through cellular processes in the body, the integumentary system regulates the body temperature, the hypothalamus - hunger and thirst of the individual and other interrelated organ systems that make the body healthy and in the state of equilibrium. Now, when diseases or disorders appear they disrupt the organ systems in the body thus, causing imbalance state - high fever, inability to focus and etc.