At the beginning of the play the Duke gives Angelo the responsibility to rule while he goes away, .
"In our remove, be thou at full ourself.
Mortality and mercy in Vienna.
Live in thy tongue, and heart." .
With this power he reinforces old laws that had "slept" while the Duke had been in power. Angelo proposes not to "make scarecrow of the law" and decrees punishment of death to any man who commits fornication or who has engaged in adulterous behaviour. In the Old Testament, the Mosaic Law had said, "If a man commits adultery with another man's wife [a woman who is not his wife] [he] must die." Leviticus 20:10. Although this reflects teachings of the New Testament (Corinthians 7) where each man should only have his own wife, he does not show the mercy that is also preached, "Blessed are the merciful for they will be shown mercy (Matthew 5:7 The Beatitudes). In the New Testament (John 8:3-11), Jesus waives the death sentence for a similar sin and shows mercy. Angelo does not show mercy but only practises the laws of the Old Testament. "Eye for eye, tooth for tooth, foot for foot" Exodus 21:24. He does not achieve the balance between mercy and law. .
Angelo's rigid interpretation of the law with no understanding of humanity can be seen when Isabella pleads with him to spare her brother's life. "Yes: I do think that you will pardon him, / And neither heaven nor man grieve at the mercy. His replies to her pleadings are short and abrupt, "He's sentanc"d, "tis too late." Through Isabella's continued pleas he is moved by her beauty and purity, "For I am that way going to temptation." Angelo becomes disturbed at his realisation of his emerging strong sexual desire. His turmoil can be seen in his soliloquy at the end of Act 2 Scene 2 as he reveals his awareness of his lust for Isabella. "What's this? What's this? Is this her fault, or mine?" The iambic measure in this first line of his soliloquy emphasises the words "this", "fault" and "mine", highlighting that he feels it is his own fault for his temptation.