[361.] Grant they be so: a concessive clause = granted that the evils turn out to be what you imagined. The alternative is given in l. [364].
[362.] What need, etc., i.e. why should a man anticipate his hour of sorrow. ‘What’ = for what (Lat. quid): comp. l. [752]; also On Shakespeare, 6, “What need’st thou such weak witness of thy name?” On the verb need Abbott, § 297, says: “It is often found with ‘what,’ where it is sometimes hard to say whether ‘what’ is an adverb and ‘need’ a verb, or ‘what’ an adjective and ‘need’ a noun. ‘What need the bridge much broader than the flood?’ M. Ado, i. 1. 318; either ‘why need the bridge (be) broader?’ or ‘what need is there (that) the bridge (be) broader?’”
[363.] Compare Hamlet’s famous soliloquy, “rather bear those ills we have,” etc.; and Pope’s Essay on Man, “Heaven from all creatures hides the book of fate,” etc.
[366.] to seek, at a loss. Compare Par. Lost, viii. 197: “Unpractised, unprepared, and still to seek.” Bacon, in Adv. of Learning, has: “Men bred in learning are perhaps to seek in points of convenience.”
[367.] unprincipled in virtue’s book, i.e. ignorant of the elements of virtue. A principle (Lat. principium, beginning) is a fundamental truth; hence the current sense of ‘unprincipled,’ implying that the man who has no fixed rules of life is the one who will readily fall into evil. Comp. Sams. Agon. 760, “wisest and best men ... with goodness principled.”
[368.] bosoms, holds within itself. The nom. is ‘goodness.’ ‘Peace’ is governed by ‘in,’ l. [367].
[369.] As that, etc. This is an adverbial clause of consequence to ‘unprincipled’; in modern English such a clause would be introduced by ‘that,’ and in Elizabethan English either by ‘as’ or ‘that.’ Here we have both connectives together. single: see [note], l. 204. noise, sound.
[370.] Not being in danger, i.e. she not being in danger: absolute construction. This parenthetical line is equivalent to a conditional clause—‘if she be not in danger, the mere want of light and noise need not disquiet her.’
[371.] constant, steadfast.
[372.] misbecoming: see [note] on ‘misused,’ l. 47. plight, condition. Skeat derives this word from A.S. pliht, danger; others connect it with pledge. It is distinct from plight, l. [301].