Why 怕 is afraid or fear?
「怕」 (Mandarin Pinyin: pà, Zhengzhang OC: /*pʰraːɡs/, to be afraid) is comprised of two components:

「心・忄」 (heart &gt; emotions), a meaning hint; and
「白」 (Mandarin Pinyin: bái, Zhengzhang OC: /*braːɡ/), a sound hint.


Note that words have both meaning and sound, and you can't write every word with just a bunch of symbols representing meaning - sounds play a major role in determining what a word is.
Here, 「白」 is only a sound hint, not a meaning hint. To emphasise that 「白」 is only a sound hint, people have written the word represented by 「怕」 differently throughout the ages with different sound hints. For example,


Sound hint 「霸」 (Mandarin Pinyin: bà, Zhengzhang OC: /*praːɡs/)


Sound hint 「巴」 (Mandarin Pinyin: bā, Zhengzhang OC: /*praː/)