*Please provide the Act and Scene (and even line numbers) when possible. This makes it easier to find within the play.
"For naught so vile that on the earth doth live
But to the earth some special good doth give;
Nor aught so good but, strained from that fair use,
Revolts from true birth, stumbling on abuse." (II.iii.17-20)
In this scene, Friar Lawrence is commenting on the plants and herbs he is gathering. The friar is in awe of the properties that plants, herbs, and stones have. The friar's knowledge of such natural elements shows that natural elements have both good and bad properties. Even if the plant or herb has poisonous (bad) qualities ("Naught so vile"), it also provides the earth with good, beneficial elements ("But to the earth some special good doth give"). Even though it can be used for good, it's properties are sometims twisted (strained) from being used positively and misused ("Revolts from true truth, stumbling on abuse").
Literary devices: a pair of rhyming couplets (live/give; use/abuse)
A very poor, facile, superficial and obvious answer from lmillerl. Think about this in context of the battle between the Capulets and Montagues, in particular Romeo's attempt to ease strife with Tybalt, who can not see beyond his historic grievance and presumption about the character of his enemies. In every being, in every person, in every moment lies the seed of transformation, of potential goodness, of hope and a positive future, if we can but nurture it properly, beyond the inclination to do harm, the negative characteristics. However, the challenge is difficult and fraught with peril. And despite best intentions, and even a positive and pure nature, there is a threshold of suffering that will twist the most altruistic, most generous soul to its own seeds of rage, destructiveness and evil. Not only Shakespeare spoke of this duality - it forms the core of most human theological traditions, that the most devilish contain the light of God, the seed of a potential angel, and the most angelic their opposite, the capacity to do great harm. Those who study crime and human violence recognize that, only by seeing this potential within each of us can we truly create a society free of the "lesser angels of our nature" and while Romeo understands that Juliette, being his love, has cast into doubt his image of the enemy, he is unable to convince Tybalt, who kills Mercutio, to which Romeo's own devils react, despite his angelic intent, and this sets of the series of events that end in ultimate tragedy.