Macbeth, Act I, Scene VII [If it were done when 'tis done]

Enter Macbeth. If it were done when 'tis done, then 'twere well It were done quickly: if the assassination Could trammel up the consequence, and catch With his surcease success; that but this blow Might be the be-all and the end-all here, But here, upon this bank and shoal of time, We'ld jump the life to come. But in these cases We still have judgment here; that we but teach Bloody instructions, which, being taught, return To plague the inventor: this even-handed justice Commends the ingredients of our poison'd chalice To our own lips. He's here in double trust; First, as I am his kinsman and his subject, Strong both against the deed; then, as his host, Who should against his murderer shut the door, Not bear the knife myself. Besides, this Duncan Hath borne his faculties so meek, hath been So clear in his great office, that his virtues Will plead like angels, trumpet-tongued, against The deep damnation of his taking-off; And pity, like a naked new-born babe, Striding the blast, or heaven's cherubim, horsed Upon the sightless couriers of the air, Shall blow the horrid deed in every eye, That tears shall drown the wind. I have no spur To prick the sides of my intent, but only Vaulting ambition, which o'erleaps itself And falls on the other.