So far, I have assumed that "often" (the third substitution in the amended quotation) is the best representative that can be found for the "of a" of the original; and inasmuch as it is confirmed by general consent, and is moreover so redundant, in this place, that its absence or presence scarcely makes any difference in the sense, it is not easily assailable.
The best way, perhaps, to attempt to supplant it is to suggest a better word—one that shall still more closely resemble the original letters in sound and formation, and that shall, in addition, confer upon the sense not a redundant but an effective assistance. Such a word is offer: it is almost identical (in sound at least) with the original, and it materially assists in giving a much clearer application to the last line.
For these reasons, but especially for the last, I adopt offer, as a verb in the infinitive ruled by doth, in the sense of causing or compelling; a sense that must have been in familiar use in Shakspeare's time, or it would not have been introduced into the translation of Scripture.
In this view the meaning of the passage becomes, "The base doth the noble offer doubt, to his own scandal"—that is, causes the noble to excite suspicion, to the injury of its own character.
Examples of do in this sense are very numerous in Spenser; of which one is (F.Q., iii. 2. 34.):
"To doe the frozen cold away to fly."
And in Chaucer (Story of Ugolino):
"That they for hunger wolden do him dien."
And in Scripture (2 Cor. viii. 1.):
"We do you to wit of the grace of God."