首楞嚴義疏注經 1.157

1.157

迷自本真也。無始晦殊，故曰不知。不生不滅，名為常住。離諸偽妄，靈鑒不昧，故曰真心。三德具足為一切法之所依止，故云性淨明體。眾生悉爾故曰皆由。

This is being deluded about one's own fundamental reality. Because it has been obscured and confounded from beginningless time, it is said that they 'do not know.' Being unarisen and unceasing, it is called 'permanently abiding.' Free from all falsities and deluded errors, its spiritual discernment unobscured, it is called the 'true mind.' Complete with the three virtues, it serves as that upon which all phenomena rely; hence it is called 'the naturally pure and luminous essence.' Because sentient beings are all like this, it says 'entirely because.'