Carry a text over, and you copy it. Copy it, and you write it. It is also why a photograph is 写真, literally a truth carried over. This is the single most useful thing a beginner can learn about kanji. A huge share of them are built exactly like this: one part for the meaning, one part purely for the sound. Hunt for a reason the magpie "means" writing and you will tie yourself in knots, because it does not. Knowing which parts carry meaning and which are just sound is the real skill.