Heretics are not only deviating from biblical orthodoxy they are also deviating from biblical orthopraxy at the same time. Calvin's letter to Laelius Socinus illustrates this well:
Certainly no one can be more averse to paradox than I am, and in subtleties I find no delight at all. Yet nothing shall ever hinder me from openly avowing what I have learned from the Word of God; for nothing but what is useful is taught in the school of this master. It is my only guide, and to acquiesce in its plain doctrines shall be my constant rule of wisdom.
Would that you also, my dear Laelius, would learn to regulate your powers with the same moderation! You have no reason to expect a reply from me so long as you bring forward those monstrous questions. If you are gratified by floating among those airy speculations, permit me, I beseech you, an humble disciple of Christ, to meditate on those things which tend towards the building up of my faith.
...And in truth I am very greatly grieved that the fine talents with which God has endowed you, should be occupied not only with what is vain and fruitless, but that they should also be injured by pernicious figments.
What I warned you of long ago, I must again seriously repeat, that unless you correct in time this itching after investigation, it is to be feared you will bring upon yourself severe suffering.
I should be cruel towards you did I treat with a show of indulgence what I believe to be a very dangerous error. I should prefer, accordingly, offending you a little at present by my severity, rather than allow you to indulge unchecked in the fascinating allurements of curiosity.
Letters of John Calvin, No. 30 (Banner of Truth), p. 128-9
Are you content with God's Word?
Are you content with the limits this places on your knowledge and with how you gain it?