Why do viruses show the properties of a living organism only after they enter the cells?

This is due to the fact that viruses have a very simple structure. Most viruses only have DNA and a protein coat that protects genetic information. For a long time, they can stay in a state of sleep in the environment, fluids, and the like. But as soon as they enter the body, they begin to show signs of life, as they receive all the necessary conditions for life. They multiply and destroy the cells of the host’s body. Some viruses are easily destroyed by leukocytes, and some are stronger for the host’s immunity.