no more than在此用作副词，= only 仅仅、只、不过是

Money is no more than our servant. 金钱不过是我们的仆人。

no more than a craft comprehensible perfectly only to the craftsman.

= only a craft comprehensible perfectly only to the craftsman. 划线部分为形容词短语作后置定语：不过是只有手工匠人才能完全理解的手工艺品。