Vincent's NT Word Studies
17. In your law (en tw nomw tw umeterw). Literally, in the law, that which is yours. Yours has an emphatic force: of which you claim a monopoly. See vii. 49.It is written (gegraptai). The perfect tense: it has been written, and stands written. The common form of citation elsewhere, but used by John of the Old Testament scriptures only here. His usual form is gegrammenon ejstin, the participle with the finite verb, literally, it is having been written.
The witness of two men. See Deut. xix. 15.
The Father - beareth witness of me. Thus there are two witnesses, and the letter of the law is fulfilled.