Ante-Nicene Fathers, Vol IX:
Epistle to Gregory and Origen's Commentary on the Gospel of John.: Chapter XX

20.  The Difference Between Not Being “Sufficient” And Not Being “Worthy.”

John records that the Baptist said he was not worthy, Mark that he was not sufficient, and these two are not the same.  One who was not worthy might yet be sufficient, and one who was worthy might not be sufficient.  For even if it be the case that gifts are bestowed to profit withal and not merely according to the proportion of faith, yet it would seem to be the part of a God who loves men and who sees before what harm must come from the rise of self-opinion or conceit, not to bestow sufficiency even on the worthy.  But it belongs to the goodness of God by conferring bounties to conquer the object of His bounty, taking in advance him who is destined to be worthy, and adorning him even before he becomes worthy with sufficiency, so that after his sufficiency he may come to be worthy; he is not first to be worthy and then to anticipate the giver and take His gifts before the time and so arrive at being sufficient.  Now with the three the Baptist says he is not sufficient, while in John he says he is not worthy.  But it may be that he who formerly declared that he was not sufficient became sufficient afterwards, even though perhaps he was not worthy, or again that while he was saying he was not worthy, and was in fact not worthy, he arrived at being worthy, unless one should say that human nature can never come to perform worthily this loosing or this bearing, and that John, therefore, says truly that he never became sufficient to loose the latchets of the Saviour’s shoes, nor worthy of it either.  However much we take into our minds there are still left things not yet understood; for, as we read in the wisdom of Jesus, son of Sirach, 4913 “When a man hath done, then he beginneth, and when he leaveth off, then he shall be doubtful.”

Footnotes

Ecclesiasticus 18.7.