Mrs. Lynde’s letters to Anne are full of Biblical allusions. Mrs. Lynde uses a semi-Biblical phrase, warning Anne not to trust strangers because “outwardly they may be as whited sepulchers and inwardly as ravening wolves” which is similar to the quotation is found in Mathew 23:27.

I don’t believe any but fools enter the ministry nowadays,” [Mrs. Lynde] wrote bitterly. “Such candidates as they have sent us, and such stuff as they preach! Half of it ain’t true, and, what’s worse, it ain’t sound doctrine. The one we have now is the worst of the lot. He mostly takes a text and preaches about something else. And he says he doesn’t believe all the heathen will be eternally lost. The idea! If they won’t all the money we’ve been giving to Foreign Missions will be clean wasted, that’s what! Last Sunday night he announced that next Sunday he’d preach on the axe-head that swam. I think he’d better confine himself to theBible and leave sensational subjects alone. Things have come toa pretty pass if a minister can’t find enough in Holy Writ to preach about, that’s what. What church do you attend, Anne? I hope you go regularly. People are apt to get so careless about church-going away from home, and I understand college students are great sinners in this respect. I’m told many of them actually study their lessons on Sunday. I hope you’ll never sink that low, Anne. Remember how you were brought up. And be very careful what friends you make. You never know what sort of creatures are inthem colleges. Outwardly they may be as whited sepulchers and inwardly as ravening wolves, that’s what. You’d better not have anything to say to any young man who isn’t from the Island.

-Anne of the Island ch.5

Matthew 23:27
King James Bible

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.

Source

King James Bible