From Milton Terry’s Biblical Hermeneutics, pg. 415-416:
This process requires, especially, three things: (1) That we be able clearly to discriminate and determine what are symbols and what are not; (2) that the symbols be contemplated in their broad and striking aspects rather than their incidental points of resemblance; and (3) that they be amply compared as to their general import and usage, so that a uniform and self-consistent method be followed in their interpretation.
A failure to observe the first of these will lead to endless confusion of the symbolical and literal. A failure in the second tends to magnify minute and unimportant points to the obscuring of greater lessons, and to the misapprehension, oftentimes, of the scope and import of the whole….A care to observe the third rule will enable one to note the difference as well as the likeness of similar symbols, and save him from the error of supposing that the same symbol, when employed by two different writers, must denote the same power, person, or event.