As many sayings, it’s quite hard to get at first, because of its archaisms. It means that every effort made towards knowing them is a way to show interest in them, therefore honoring them. The difficulty can arise from the fact that Comme can have many meanings, and here we have an usage of the term that expresses the mode or manner of the action, but is somewhat slightly causal also.
On a side note, another saying has nearly the same grammatical form :
« Comme on fait son lit, on se couche. »
Edit : For the ses saints part, the possessive can be unsettling, I admit. It doesn’t refer to someone‘s saints or the interlocutor‘s saints, but to one‘s saints, it’s a reflexive form (like in my example above, son lit). This kind of possessive can be assimilated to the one we have in :
« Je connais mes classiques. »
These classics (implied : classic books) aren’t in any way “mine”, but it’s meant to refer to the relation I have with them, not them directly. Also, the proverb itself belongs to a time in which religion and faith were much more “alive”. Not everyone prayed each saint equally. There were saints attached to certain skills or jobs, some others revered in a region or town more than elsewhere…
An English translation of the literal meaning would be “As we know our saints, so do we honor them.” The word comme here indicates likeness: the sentence could also be expressed (less idiomatically) by “On honore ses saints autant qu’on les connaît”.
The French saying takes worship of the saints as a virtue. This comes from the Catholic religion. It expresses that knowing the saints is a large part of honoring them. The English saying uses a different example: knowing one’s friend, and respecting them. The two examples both express the opinion that it is important to know and understand the people or abstractions¹ that we are supposed to respect and honor.
There is a large number of Catholic saints, and most people only worship a handful. Thus ses saints, rather than les saints: these are the saints that one is supposed to honor. The literal grammatical construction uses the impersonal pronoun on (classified as pronom indéfini in French). This is a concept that English doesn’t use much, but could express as “As one knows one’s saints, so does one honor them”. The possessive pronoun ses here refers to the impersonal pronoun on.
¹ In the case of saints, the worship is more for the concept that the saint represents than the actual person.
Si l’on comprend ses saints comme un substantif,
Comme on connait le bien, on le pratique.
C’est le même mouvement qui relie une pensée aux actions adéquates.