Avraham Avinu has gone through this gut-wrenching test of
the Akeyda and he returns home to his life long partner Sarah Imeynu and discovers that in his absence, she has passed away. Although Hashem promised him the entire land, at this moment, he does not even have a 20 square foot plot to bury his wife. He approaches the locals and asks for permission to
purchase the cave of Machpela.  

Midrashim tell us that he discovered earlier that this
was the burial place of Adam and Chava and had some spiritual portal connecting
the worlds.  

Efron makes an empty offer of giving it to Abraham at no
charge and then continues, 'My Lord, heed me! Land worth four hundred silver
shekels, between me and you - what is it? Bury your dead.' Our rabbis explain
that this was an exorbitant price. Still the pasuk continues ….  

וַיִּשְׁמַ֣ע אַבְרָהָם֮ אֶל־עֶפְרוֹן֒ וַיִּשְׁקֹ֤ל
אַבְרָהָם֙ לְעֶפְרֹ֔ן אֶת־הַכֶּ֕סֶף אֲשֶׁ֥ר דִּבֶּ֖ר בְּאׇזְנֵ֣י בְנֵי־חֵ֑ת
אַרְבַּ֤ע מֵאוֹת֙ שֶׁ֣קֶל כֶּ֔סֶף עֹבֵ֖ר לַסֹּחֵֽר׃  

Abraham accepted Ephron’s terms. Abraham paid out to
Ephron the money that he had named in the ears of the Hittites—four hundred
shekels of silver at the going merchants’ rate. 

Baal HaTurim: לעפרן חסר בגימטריא עין רע. 

Kli Yakar  

The name עפרן is missing a 'ו'. The Ba'al Haturim explains
that he had an evil eye, and the name of עפרן without a 'ו' adds in gematria to
ר״ע עי״ן (evil eye). The reason for this comes from a statement in Bava Batra (9B) which states that
whoever gives a coin to a poor person is blessed with 6 blessings, and whoever
is stingy with the poor is not blessed with these 6 blessings. It is for this
reason that Efron lost his 'ו' (which has the numerical value of 6) - as he was
stingy, he lost 6 blessings.  

Our sages also tell us (Sotah
36B) that we give the glass of blessing to a generous spirit, as the verse
states טוב עין הוא יבורך (with a 'ו') - Don't read 'he is blessed', but rather
'he will bless'.  

Both the literal reading and the way it is read are true -
someone who blesses others generously will be blessed with the six blessings
(as depicted by the 'ו' in יבורך). 

Furthermore, know that the numerical value of רע עין = 400.  

We find 400 in 4 different places specifically with regards
to stingy people. The first is Efron who was stingy and therefore took 400
Silver shekels.  

The second place relates to the brothers of Joseph had a bad
view of Josef the righteous and they were jealous of him because of the coat of
many colours. The result of this was that the Jewish people were exiled for 400
years as strangers, affliction and servitude.  

The third place relates to Esau who had a bad view of his
brothers, and he was jealous of him because of the blessings which Isaac
blessed Jacob. It is for this reason that Jacob placed a space between each
flock to fill the eyes of that evil man (that was to be given to Esau), because
he came with 400 men.  

The fourth place relates to Naval, because he was a stingy
man. It was for this reason that David approached him with 400 men.