In chapter 3 of the Path of the Just, the Ramchal says:
He who wants to watch over himself must investigate two matters.
- The first: that he contemplate what is the true good for man to choose and what is the true evil for him to flee from.
- The second: on the actions which he does, to determine if they are in the category of the good or the evil.
This applies both to times when he is in the act of doing and when not in the act of doing.
- When in the act of doing: that he not do any act without first weighing it on the scales of this understanding.
- Not in the act of doing: that he bring up before himself the remembrance of his deeds in general and weigh them, likewise, in these scales to determine what they contain of evil in order to cast it away and what of good, in order to perpetuate it and strengthen himself in it. If he finds in them of the evil, he should then contemplate and investigate, reasoning out a strategy to employ in order to turn away from that evil and cleanse himself of it....
then later on says
Our sages of blessed memory taught us explicitly the need for this accounting as they said: " 'therefore the rulers say, let us enter into an accounting' (Numbers 21:27). Therefore the rulers - of their [evil] inclinations said come and consider the accounting of the world - the loss incurred by doing a mitzva against the gain earned through it, and the gain obtained by doing a sin against the loss incurred..."
how is this an "explicit" instruction of what he said previously?
the former is about examining one's personal deeds whereas this is about weighing generally the reward/loss of a mitzva against a sin