The term “whited sepulcher” is used when Matthew complains about having Reverend Bulkeley in his house. He gives the following rant:
"He is a hypocrite and a whited sepulcher!" Matthew's fist crashed down on the table. "And I’ll have no more texts read at me in my own house!" (Ch. 6)
A “whited sepulcher” is a Biblical allusion. It is a reference to Matthew 23:27, and it means "hypocrite." The verse in the Bible reads like this:
Woe unto you, scribes and Pharisees, hypocrites! for ye are like unto whited sepulchres, which indeed appear beautiful outward, but are within full of dead men's bones, and of all uncleanness. (King James Bible)
A sepulcher is a tomb, and the “whited” part means whitewashed. It literally means whitewashed tombs. The phrase says the tombs look decent on the outside but are actually full of bones. Thus, the term “whited sepulcher” came to be a term for a hypocrite.
Why is Matthew so upset about having this man in his house? Rachel says that Bulkeley is “is a good man, just set in his ways” (Ch. 6), but Reverend Bulkeley is loyal to the king. Matthew, on the other hand, has objections to the king. There is revolution stirring in the colonies, and in Wethersfield not everyone is in agreement. This is why Matthew calls Bulkeley a hypocrite, because he claims to be a man of God but uses religion to hide his argument.
The word "implacable" can be found in Chapter 7 when Kit is describing her visits with William.
A second Saturday passed, a third and a fourth, and William's calls fell into a pattern. I shall ask Mercy to teach me to knit, Kit decided after the second Saturday, and thereafter she armed herself with wool and needles. At least they kept her hands occupied and gave her an excuse for not meeting that implacable gaze. (Ch. 7)
When Kit calls William’s gaze “implacable” she means that he seems to keep staring at her without stopping. In fact, all they seem to do is sit quietly. Kit feels uncomfortable, and does not really understand William’s game. This is why she decides to knit, because she wants to have something to do while they are just sitting there.
The word “reckon” means to deal with or face up to. Matthew uses this term in defending Kit when she is accused of consorting with Hannah to be complicit in Mercy’s sickness.
"Begone from my house!" he roared, his caution drowned in anger. "How dare you speak the name of a good, God-fearing girl? Any man who slanders one of my family has me to reckon with!" (Ch. 17)
William stands up for Kit because she is his responsibility. Of course he does not approve of her being with Hannah. Her actions affect his reputation, and when he finds out what has been happening he is upset. The entire situation blows up out of proportion though. People are frightened, and they think that Hannah is a witch and making people sick. They accuse Kit of witchcraft too.