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God: "I looked for someone to take a stand for me, and stand in the gap" (Ezekiel 22:30)

A doctrine is what the whole Bible teaches us today about some particular topic. This definition is directly related to...systematic theology, since it shows that a 'doctrine' is simply the result of the process of doing systematic theology with regard to one particular topic (Wayne Grudem and Jeff Purswell).
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Whenever a man takes upon him to make additions to the Scriptures, he is likely to end with valuing his own additions above Scripture itself.
J.C. Ryle