I pick it apart and put it down,
the thoughts I used to get high
(to you, (from) hereafter:
for you, an eye’s kept out)
but it lives in my heart, singing;
I earn it—my soul—and straight fly.
The use of the plural “thoughts” here pertains to eloquence or diction and points to a principle*: subject-verb agreement can flex for rhetorical effect. In the above example case, grammaticality would render: “thought I use”, in accordance with number, while the use of the plural follows the action of something coming apart; the poet reflects disregard for “an” object, favoring “his” subject—with each line the poet addresses each moment. This disregard for anything that is not the poet’s aim is further substantiated by a tone of lament, seemingly for the passed moment, which carries through the second line.
The line end here is a stunt in layman terms, or it is simple enjambment; the poet draws one to one meaning, which stands alone before the next lines, but leads to another by the use of a conspicuous phrase.
Perhaps the parentheticals illustrate the attained and consequently furthered from a perspective depth of sky, we may reserve it for the poet. The colon characteristically depicts (the defining of) offering, while the two uses of “you” serve to single out and praise. The use of you also relates to the earlier plural use in reflecting the poet’s desire for singularity over division of love or wholesomeness over everything, all else being separable.
The poet diverts his speech, finally, from object to subject to audience, first revealing to them his aim and subject of choice, who all seem to be entangled.
However, the usage of the conjunction “but” implies that the first two lines were directed to the audience as well, and that the greater middle parenthetical could be omitted altogether. This would relate the new meaning of newfound will and control, that the mind’s elation is not satisfying alone, an aim, a target is essential.
The ambiguous pronoun “it” is chosen, purposefully, most likely, to reflect the shift in perspective and direction, and the ambiguity of the central lines. Although the final dashed parenthetical seems to reveal what “it” is as the soul, it may be the love, the eye or the thoughts themselves, the device simply serving as another quick re-direction.
Perhaps the key lay in the central phrase “an eye’s kept out”. If one were to truly address his soul, he may wonder what it could possibly be unaware of that one would have to keep an eye out for its sake. Unless of course the soul, being a transient thing, is only made whole, as it were, and singing, by the active effect of the mind, conscious of its heart which, like an abode one travels to and from, preserves the memory and station of all it houses.
The essential metaphor here lay within the notion of flight and height. That is, that the mind—or anything—can often be used as a means by which one becomes elevated, in the sense one aims for something afar—whatever it may be—and though it lay with us in all.
*A note regarding the legitimacy of “principles of eloquence and rhetoric”: such usage of language does not warrant grammar obsolete nor absolve adherence to proper syntax, it is mere poetic license of which reason and logic are the authority**. Without the action of “pick apart”, the line would be made weaker, though were it taken away completely, the line may retain the meaning of recollection and lament.
**A further note regarding an authority over poetic license: it is not to say that reason and logic are used to employ poetic license, but rather that the poet is excused after the fact; principles are derived through observation but do not dictate a course of action, they merely set the stage, so to speak, or establish an environment.