The soliloquy you speak of is in Act II, scene iii. Friar Lawrence comments on the ability of plants to be both helpful and hurtful, healthy and poisonous. People are the same way, one moment benevolent (kind) and the next violent or angry or destructive. He also notes that, like with plants, there is variety in the kinds of people on Earth. Here is the passage from the play:
And from her womb children of divers kind
We sucking on her natural bosom find;
Many for many virtues excellent,
None but for some, and yet all different.
O, mickle is the powerful grace that lies
In plants, herbs, stones, and their true qualities:
For naught so vile that on the earth doth live
But to the earth some special good doth give;
Nor aught so good but, strain'd from that fair use,
Revolts from true birth, stumbling on abuse:
Virtue itself turns vice, being misapplied;
And vice sometimes by action dignified.
Within the infant rind of this small flower
Poison hath residence, and medicine power:
For this, being smelt, with that part cheers each part;
Being tasted, slays all senses with the heart.
Two such opposed kings encamp them still
In man as well as herbs,--grace and rude will;
And where the worser is predominant,
Full soon the canker death eats up that plant. ...... Good luck