From Core Rulebook (p. 303):
Focus: A focus is an object that funnels the magical energy of the spell. The spell gains the manipulate trait and requires you to either have a free hand to retrieve the focus listed in the spell or already be holding the focus in your hand. As part of Casting the Spell, you retrieve the focus (if necessary), manipulate it, and can stow it again if you so choose.
And from Compoment Substitution section, on the same page:
If you’re a cleric Casting a Spell from the divine tradition while holding a divine focus (such as a religious symbol or text), you can replace any material component the spell requires by using the divine focus as a focus component instead. Unlike the normal rules for a focus component, you can’t retrieve or stow the focus when making this substitution.
I am having trouble understanding why the "retrieve", "manipulate" and "stow" verbs are mentioned separately and what do they mean in this specific context. Also, why is it explicitly mentioned that you can't do those things ("retrieve" and "stow") if you are a cleric and you use your holy symbol as substitution? Does this somehow affect you, your religious symbol, your spell or anything else?
Could anyone provide some clarification or point me to a related page from the rulebook?