《礼记·祭义》
如果孝子对父母有深深的爱戴，心中就必然充满和顺之气；·心中充满和顺之气，脸上就一定会表现为和颜悦色；脸上有和颜悦色，就一定会表现为曲意承欢的样子。
孝子之有深爱者，必有和气；有和气者，必有愉色；有愉色者，必有婉容。
If a filial son deeply admires his parents, he will be filled with a harmonizing energy; a heart filled with a harmonizing energy will certainly show a friendly expression on the face; and a person with a friendly expression on their face will certainly behave in a way that shows great care and respect to others.