If he had said, "Whoever loves God knows what must be known, and knows as he ought," then this would fully answer and satisfy the expectation.
But he says, "Whoever loves God is known by Him," εγνωσται υπ αυτου.
In Russian it is translated, "to him knowledge is given by Him," but it is obvious that this does not correspond to the original. The Slavonic translation is the correct one.
What, then, does it mean to be known by God?
Since God knows all things, when it is said that someone is known by God, some special kind of knowledge must be understood here.
It is like someone who sees everything, but looks especially at one thing.
The Prophet says, "The Lord knows the way of the righteous." This means that He looks upon it with special attention, guards it, and especially cares for it.
This is clear from what follows: "but the way of the ungodly shall perish," as though abandoned without the Lord's attention.
In this way God also knows the one who loves Him. He knows him by caring for him especially, or, what is the same, by loving him.
The result is this: whoever loves God is known by Him, that is, he stands under His special care as one who belongs to Him and is loved by Him.
If the one who loves God lives in God, then God, by Whom the one who loves Him is beloved, dwells in him.
He who loves God abides in God, and God abides in him. Is this not what the Apostle wished to say?
We are accustomed to value knowledge far too highly. We think that the Apostle, having rebuked our knowledge, must point out the paths to it.
But the Apostle's whole concern is with life, not with knowledge.
Therefore, having rebuked knowledge, did he not have this in mind? Knowledge alone, without love, inflates, and moreover it does not exist in perfection.
Someone will ask: what then should be done, and where shall one take knowledge?
I will tell you this: abandon all cares about knowledge. Love God, and you will be loved by Him. That is all.
Here is your goal. There is nowhere further to go, and nothing greater to desire.
Blessed Theodoret writes: "We need much knowledge, and in the present life it is impossible to acquire perfect knowledge.
Therefore let us love God, that we may be made worthy of His providential care for us.
This is what the Apostle expressed in the words, 'Whoever loves God is known by Him,' that is, he is made worthy of His care.
So also blessed Moses said to the God of all: 'You have said to me, You have found grace before Me, and I know you above all'" (Ex 33:12-17).
Blessed Theophylact follows the same path and brings one also to knowledge: "This is what the Apostle says here: whoever loves his neighbor certainly loves God as well.
The one who loves God is known by Him, that is, he is made known to Him as His own, as one of His household.
Having become so closely known to God, he receives knowledge from Him, although even then he possesses it imperfectly.
Thus, even if you have knowledge, do not be exalted, for it is imperfect. And this imperfect knowledge is not yours, but God's gift.
Do you see how the Apostle humbles their arrogance?"