俱舍論頌疏論本 23.18

23.18

如是二善根，皆初法後四者，煗、頂二善根初安足時，皆法念住。後增進時，通四念住。初安足者，謂此煗、頂以十六行相，最初遊踐四聖諦迹，名初安足，即初起也。謂見道中唯法念住，以煗、頂位順見道故，故初安足唯法念住。後增進時，稍容預故，故得通修四念住也。

As for "These two roots of goodness both [begin with] dharmas first and later the four": when the two roots of goodness of warmth and summit first gain a foothold, they are both the application of mindfulness to dharmas. Later, when advancing, they extend to all four applications of mindfulness. 'First gaining a foothold' means: when these [stages of] warmth and summit, with the sixteen modes, first step upon the traces of the four noble truths, this is called 'first gaining a foothold', which is their initial arising. That is to say, within the path of seeing there is only the application of mindfulness to dharmas; and because the stages of warmth and summit accord with the path of seeing, their initial foothold is solely the application of mindfulness to dharmas. Later, when advancing, because there is slightly more leisure, they are able to cultivate all four applications of mindfulness.