It is right to only attempt to do Christian theology after the recognition that Deus dixit (‘God has spoken’). Herman Bavinck, and Karl Barth after him, in their own ways recognized this reality and proceeded in their theologizing accordingly (if you would like to read where Barth develops this then tolle lege his Göttingen Dogmatics). George Hunsinger, as he is engaging with this theme in general (while sketching the thinking of Irenaeus and Hilary), and doing so while engaging with Barth’s theology in particular provides an excellent quote from Hilary,
Human feebleness cannot by any strength of its own attain to the knowledge of heavenly things; the faculties which deal with bodily matters can from no notion of the unseen world. Neither our created bodily substance, nor the reason given by God for the purposes of ordinary life, is capable of ascertaining and pronouncing upon the nature and work of God. Our wits cannot rise to the level of heavenly knowledge, our powers of perception lack the strength to apprehend that limitless might. We must believe God’s word concerning himself, and humbly accept such insight as he vouchsafes to give. We must make our choice between rejecting his witness, as the heathen do, or else believing in him as he is, and this in the only possible way, by thinking of him in the aspect in which he presents himself to us…. The meaning of words shall be ascertained by considering the circumstances under which they were spoken; words must be explained by circumstances not circumstances forced into conformity with words. (De Trin. IV.14)
For he whom we can know only through his own utterances is a fitting witness concerning himself. (De Trin. I.18)
As Barth himself writes:
§3 Deus Dixit. Christian preachers dare to speak about God. The permission and requirement to do so can rest only on their adoption of the witness of the prophets and apostles that underlies the church, the witness which is to the effect that God himself has spoken and that for this reason, and with this reference, they too must speak about God. This assumption can arise only because they take it that God’s address is directed to them as well. It means that with fear and trembling they recognize God as the true subject of the biblical witness and their own proclamation.
Don’t be fooled, this all sounds too normal and self evident; as a result you might well skim right by the radical nature of what both Barth and Hilary are asserting. It is a radical procedure to actually do what Barth says, and what Hilary speaks; radical because it usually is not done. Too often theological reflection is sublated by and conflated with philosophical theology; of the sort that conceptions about God are conceived of prior to hearing God speak. And then these philosophical conceptions are forced into a conversation with what ‘God has spoken’ about Himself in His Self revelation in Jesus Christ attested to by Holy Scripture. It becomes really hard for us, centuries removed from much of this style of theologizing to differentiate between what God has spoken to us and for us of Himself and what has been conflated with that.
We should be on guard then! If Hilary and Barth are correct then we need to really work at discerning what God has genuinely said about Himself and what the Tradition of the church says He has said of Himself. The trad, at least for Protestant Christians is not our rule of faith, Jesus Christ is (and Holy Scripture as it bears witness and finds its lively reality in Christ). This doesn’t mean that we ignore the Tradition of the church, or that it is all wrong (or wrong at all!); it simply means that like the Bereans we are to test all things by Scripture and hold fast to that which is good (to Jesus Christ). As we operate this way we must do so humbly lest we elevate ourselves over the wisdom and insight of the teachers that Christ has been bestowing on His church (Ephesians 4) ever since His ascension. We are well advised to be in conversation with the Tradition, all along understanding that what counts as the Tradition or as orthodox might well be a contrivance of philosophical conceiving with what God has spoken such that a differentiation needs to yet be made between the two. We need to be critical, and primarily in conversation with the Living Word as He intercedes for us, as He the Great Teacher teaches us. We need to operate as if we have a living moment by moment relationship with God in Christ, and realize that if we seek Him we will find Him because He is love, and because He has made Himself known to us as He has spoken His definitive word to us in His Son. This is radical even if it might not seem like it to some.
 Hilary cited by George Hunsinger, Evangelical Catholic And Reformed: Doctrinal Essays on Barth and Related Themes (Grand Rapids, Michigan/Cambridge, U.K.: William B. Eerdmans Publishing Company, 2015), 60-1 kindle.
 Karl Barth, The Göttingen Dogmatics: Instruction in the Christian Religion, Volume One (Grand Rapids, Michigan: William B. Eerdmans Publishing Company, 1991), 45.