How is the phrase "the Lord's anointed temple" a metaphor?
This phrase comes from Act II, Scene 3, and is spoken by Macduff. Having just discovered the body of King Duncan, Macduff is announcing this news to the other noblemen.
To understand this metaphor, take a look at the line in full:
Most sacrilegious murder hath broke ope
The Lord’s anointed temple, and stole thence
The life o' th' building!
This line is, therefore, a metaphor because Macduff compares Duncan's body to a church ("the Lord's anointed temple"). Specifically, Macduff is saying that somebody has broken Duncan's body and taken its life, just as a person might take something of immense importance from a church.
This metaphor is significant because it reveals Macduff's true feelings about Duncan. This reaction shows, for example, that Macduff is genuinely upset by Duncan's death. Moreover, he believes that a monarch is a person of divine importance, anointed by God, and that the murder of a king is an act of sacrilege.
Macduff is, therefore, the ideal noblemen: he is completely loyal to Duncan and feels a genuine affection for him. Notice the contrast here between Macduff and Macbeth. Macduff genuinely mourns Duncan's death, while Macbeth is the man who caused it.