Please explain the following six lines from the first sonnet of Sir Philip Sydney's Astrophel and Stella.
"But words came halting forth, wanting Invention's stay,
Invention, Nature's child, fled stepdame Study's blows,
And others' feet still seem'd but strangers in my way.
Thus great with child to speak, and helpless in my throes,
Biting my truand pen, beating myself for spite,
'Fool' said my Muse to me, ' look in thy heart and write."
As is typical in the Petrarchan sonnet, there is a turn after line 8, signalled by the word "But" at the beginning of line 9. The turn in this case is the move from problem towards solution, although the solution is not fully revealed until the last couplet.
The poet starts writing but his words are awkward and halting, unsupported by invention (ideas). Invention, for Sidney, springs from imitating nature (or, more precisely the Platonic forms) rather than imitation of imitation, and thus his study of other poets who imitate nature (and their "feet" -- i.e. meters and metrical compositions) interferes with his own ability to compose. As he berates himself for his own inability to write, his Muse (the personified source of his inspiration) tells him simply to express what he feels directly.
Much of the literary theory behind this sestet can be found in Sydney's "Defence of Poetry" which itself recapitulates a neo-platonic reading of Plato's Republic (probably via acquaintance with Ficino's translation of Proclus' commentary as well as Ficino's own direct experience of translation of Plato into Latin).