TCR 135 - Why Are Mediation, Intercession, Expiation and Propitiation Important?

TCR 135 [4, 5]

. . . what is meant in the Word by 
mediation, intercession, expiation and propitiation. 
These are the four things predicated 
of the grace of the one God in His Human. 
God the Father could under no circumstances
be approached, nor can He approach any person,
because he is infinite and in His Being (esse), 
which is Jehovah. 
If He approached anyone in that form, 
He would destroy him, 
as fire does wood, reducing it to ashes. 
This is plain from His reply 
when Moses desired to see Him: 
that no one can see Him and live (Exodus 33:20). 
The Lord too said that no one has ever seen God, 
except the Son who is in the Father's bosom 
(John 1:18; Matthew 11:27); 
and again, that no one 
has heard the Father's voice 
or seen His appearance (John 5:37).
We do read that Moses saw Jehovah face to face, 
and spoke personally with Him; 
but this was done through an angel, 
and the same happened in the cases 
of Abraham and Gideon. 
Now because such is God the Father in Himself, 
He was pleased to take upon Himself human form, 
and in this 
to allow people to approach Him, 
so as to hear them and speak with them. 
It is this Human which is called the Son of God, 
and this it is which 
mediates, intercedes, propitiates and makes expiation. 
I shall tell you therefore 
what is the meaning of those four actions 
attributed to the Human of God the Father.

-- Mediation means that the Human 
is the intermediary by means of which 
a person can approach God the Father, 
and God the Father can approach him, 
and so teach and guide him to salvation. 
This is why the Son of God, 
meaning the Human of God the Father, 
is called the Savior, 
and on earth Jesus, which means salvation. 
-- Intercession means continual mediation; 
for love itself, 
to which mercy, clemency and grace belong, 
continually intercedes, 
that is, acts as intermediary for those 
who obey His commandments, 
and whom He loves. 
-- Expiation means the removal of the sins 
into which everyone would rush, 
if he were to approach Jehovah without mediation. 
-- Propitiation means the working 
of clemency and grace,
to prevent anyone consigning himself 
to damnation through sins; 
likewise, protection against profaning what is holy. 
This was the meaning of 
the Mercy Seat above the Ark in the Tabernacle.