Why use NKJV in the public ministry?

 I firmly believe WCF 1.8

The Old Testament in Hebrew (which was the native language of the people of God of old), and the New Testament in Greek (which, at the time of the writing of it, was most generally known to the nations), being immediately inspired by God, and, by his singular care and providence, kept pure in all ages, are therefore authentical; so as, in all controversies of religion, the church is finally to appeal unto them. But, because these original tongues are not known to all the people of God, who have right unto, and interest in the Scriptures, and are commanded, in the fear of God, to read and search them, therefore they are to be translated into the vulgar language of every nation unto which they come, that, the Word of God dwelling plentifully in all, they may worship him in an acceptable manner; and, through patience and comfort of the Scriptures, may have hope.

In part, that means that though I prepare from the original languages, and sometimes highlight things from them that are more clear/emphatic in the original, I am very desirous that I not undermine folks' confidence in the English text. Translation is scripturally/theologically required.

But take a look at that this part again:

being immediately inspired by God, and, by his singular care and providence, kept pure in all ages, are therefore authentical

Authentic=preserved by God unto the church throughout the ages
Autographa=not given to us, in the wise providence of God, and not particularly related to whatever is on the oldest textual documents currently available.

Confessional Presbyterianism officially takes an Ecclesiastical (Majority) Text position over-against a Critical Text position. 

The NKJV is actually textus receptus based, which isn't quite the same thing. But, for widely available English translations, it requires the least "correction" in the New Testament text. There's more to say, when there is more time/space to be used for it.