He knew teaching was his true vocation since childhood.

vocation 来自拉丁语 vocare（召唤），词根 voc- 表示"声音、召唤"，后缀 -ation 表示状态或行为。原指"神的召唤"，现指"特别适合的职业"或"天职"，强调与生俱来的使命感和适合性。