Albert Barnes on Matthew 23:27

Like unto whited sepulchres. For the construction of sepulchres, Mt 8:28. Those tombs were annually white- washed, to prevent the people from accidentally coming in contact with them as they went up to Jerusalem, The law considered those persons unclean who had touched anything belonging to the dead, Nu 19:16. Sepulchres were therefore often whitewashed, that they might be distinctly seen. Thus "whited," they appeared beautiful; but within they contained the bones and corrupting bodies of the dead. So the Pharisees. Their outward conduct appeared well; but their hearts were full of hypocrisy, envy, pride, lust, and malice--fitly represented by the corruption within a whited tomb.

(m) "whited sepulchres" Lk 11:44, Acts 23:3