What I think is really interesting about Barth is how he goes on to talk about the nature of Christian knowledge of God in the time after Jesus' death, resurrection, and ascension, when He has promised to send His Spirit into the world and called the church to be his witnesses; to testify to His accomplishment and His revelation.
What does that mean? What is the character of that witness? What does it look like? This is where Barth really corrects some of our attitudes, both in and out of the church setting:
We can never control our knowledge of this fact and therefore our authority to speak of it. It is not our own product, but the work of that fact in its character as revelation. It does not become our possession. We cannot put it in our pocket and carry it round with us. We can only use it at once as its work takes place in its character as revelation. We are not to hoard it, any more than the Israelites could hoard the manna in the wilderness.
We can and may know that fact when it is revealed - and know it with the self-grounded certainty which corresponds to its self-grounded being and occurrence. But we should be fools - real fools in the biblical sense of the word - if either to ourselves or others we pretended to be the expert bearers of revelation, appealing for our authorisation (in our own eyes and those of others) to a knowledge of revelation which is either transmitted to us institutionally or infused personally, like the Roman Catholic to the authority of his Church, the 'Fundamentalist' to the biblical texts, and the sectarian to his inner voice.
We can and must act as those who know. But we must not claim to be those who know. For if our knowledge of this fact from its self-revelation is not new every morning, if it is not newly received from it, with empty hands, as a new gift, it is not this knowledge at all.
And its flimsiness will be quickly and radically enough exposed. Its power consists in the divine act of majesty in face of which those who really know will always find and confess that they do not know. The attitude of those who know in this power can only be one of the greatest humility. It is the necessary converse of the resoluteness with which they make use of their knowledge. It distinguishes this resoluteness from the arrogance and timidity of mere opinion and hypothesis. It respects the freedom of God, and is therefore the root of the freedom in which they make actual use of their knowledge. It leads them to pistis [faith], and therefore to gnosis [knowledge], to unceasing prayer and therefore to knowledge.
It is just because they can have no doubt as to the liberation which is quite outside their own control that those who are really free to know this matter can never lose a sense of humour in relation to themselves.Church Dogmatics IV/2, 124-125