The quote as it was used in shortened form was not "out of context", at all.
Not one tiny bit. The meaning does not change, but in fact becomes even worse when more in full.
Indeed, as if souls can correctly discern what is of God and realize assurance of Truth (including writings and men being of God) without an infallible magisterium, then it means such is not essential for that, and validates the possibility of dissent from the magisterium.
And Rome cannot have that, even if that is how the NT church began.