四分律行事鈔資持記 2.585

2.585

制意中。初二為他，意見戒緣；三是為法，四即為己。淫重由成，故云惡業次第也。

In the intention of the prohibition: The first two are for others, the intention of which is seen in the precept's origin; the third is for the Dharma; the fourth is for oneself. Heavy sensual desire comes to be through this, hence it says 'the sequential order of evil karma'.