This verse is the negative counterpart of verse 10 and at the same time elaborates verse 9b. It forms the climax in the refutation of the false teachers. These men, John points out, live in the deepest darkness (thrice mentioned), since they blindly wander about in it, act in it, and cannot see the light (although they pretended to live in it; see 1.5). The last clause reinforces and explains the two preceding ones, showing why they cannot but wander about and act in darkness. With the exception of the last one, the verbs in this verse are in the present tense with durative force.

He … does not know where he is going, or ‘he is not aware in what direction he is going (or which road he is taking).’ Or, since going refers to behavior, ‘he does not realize what he ought to do.’

The darkness has blinded his eyes is a syntactic construction that may be idiomatically unacceptable in the receptor language. Some possible restructurings are ‘living in the darkness (as he is), his eyes are blinded’; compare also “to move in the dark is to move blindfold” (Phillips), or ‘his eyes can’t see because it is dark.’ The verb in this clause is in the aorist tense because it refers to the conclusion and result of a process that lasted for some time.

“To blind,” or ‘to cause to be blind,’ ‘to cause not to see’: in some receptor languages such verbs preferably take the person concerned as object, not that person’s eyes or sight; compare ‘has made him blind.’ In other languages “to blind the eyes” must be rendered by ‘to dim/block the eyes,’ ‘to take away the sight,’ ‘to cover the eyes’ (a verb that is also used in the language concerned with reference to the mind or heart), or even ‘to destroy the eyes/sight.’

Quoted with permission from Haas, C., de Jonge, M. and Swellengrebel, J.L. A Handbook on The First Letter of John. (UBS Handbook Series). New York: UBS, 1972. For this and other handbooks for translators see here .