External expresses internal

Worship means reverence and humility it means revering your real self and humbling delusions. If you can wipe out evil desires and harbor good thoughts, even if nothing shows its worship. Such form is its real form. The Lord wanted worldly people to think of worship as expressing humility and subduing the mind. So he told them to prostrate their bodies to show their reverence, to let the external express the internal, to harmonize essence and form. Those who fail to cultivate the inner meaning and concentrate instead on the outward expression never stop indulging in ignorance, hatred, and evil while exhausting themselves to no avail. They can deceive others with postures, remain shameless before sages and vain before mortals, but they'll never escape the Wheel, much less achieve any merit. ~ Bodhidharma's Breakthrough Sermon

Source:
www.purifymind.com/Sutras19.htm