Sydney’s audience knew their Roman mythology. Cupid is the son of Venus and Mars. The conceit is that Stella is cupid’s bow, and she has an infinite amount of ammunition.
I am, as usual, not altering the text: this is Elizabethan English
His mother deere, Cupid offended late,
Because that Mars, growne slacker in her loue,
With pricking shot he did not throughly moue
To keepe the place of their first louing state.
The boy refusde for fear of Marses hate,
Who threatned stripes if he his wrath did proue;
But she, in chafe, him from her lap did shoue,
Brake bowe, brake shafts, while Cupid weeping sate;
Till that his grandame Nature, pitying it,
Of Stellaes brows made him two better bowes,
And in her eyes of arrows infinit.
O how for ioy he leaps! O how he crowes!
And straight therewith, like wags new got to play,
Falls to shrewd turnes! And I was in his way.
Sir Philip Sydney