In the first few lines of this soliloquy, Macbeth considers "If it were done when 'tis done, then 'twere well / It were done quickly;" What Macbeth seems to mean by this is that if the business of the murder could be finished as soon as the deed was done, it would be good to have it finished swiftly. Clearly however, such actions do have many consequences and the rest of the speech makes it clear that Macbeth is only too aware of these.
When, indeed, Macbeth refers to "bloody instructions", we can see that he realises what an immoral and terrible deed it is to murder. In my opinion, the image of these "bloody instructions" coming back to haunt "the inventor" is particularly vivid. It is also rather ironic, as this is exactly what happens to himself and Lady Macbeth later in the play, especially in the banquet scene.
I think it is noticeable how, throughout the soliloquy, Macbeth avoids using the words "murder" or "death". Instead, he uses euphemisms such as "surcease", "assassination","the deed" and "taking off". I suspect that he wants to hide from himself the true meaning of his actions.
Macbeth 's internal debate continues, he looks for reasons against the murder:
"He 's here in double trust;
First, as I am his kinsman and his subject,
Strong both against the deed; then, as his host"
The theme of trust is especially evident in this short quotation. Macbeth sees he has a duty to protect Duncan, both as his kinsman and as his host. He can see that to violate this trust would be to