One root holds the whole idea of keeping something safe: to guard it, to maintain it, to preserve it. The pa'al לִשְׁמוֹר is everyday Hebrew for watching over, keeping a promise, or keeping Shabbat. Shift to the pi'el לְשַׁמֵּר and the keeping becomes deliberate, technical preservation: food, heritage, a state of things. The same three consonants spread out into a whole world of guards, watches and preservatives, but the two verbs below are the verified core. They are the same three letters seen from two angles. Every word here is verified against pealim, niqqud included.
The same root runs through the verb system. Each binyan is a voice: it bends the one idea into active, passive, causative or reciprocal. Tap to hear.
The pa'al / pi'el contrast is the lesson here. Pa'al לִשְׁמוֹר is the plain, broad act of keeping (guarding, observing, keeping a promise). Pi'el לְשַׁמֵּר intensifies it into deliberate preservation: preserving food, conserving heritage, maintaining a system. Hebrew has not lexicalized the other binyanim for this root, which is normal: not every root fills all seven.
Same root letters, different noun moulds (mishkalim). The mould tells you the function: who does it, the act of doing it, or the thing produced.
Strip the prefixes, suffixes and vowels. Three consonants remain, and the meaning lives there.