I would offer. I think a good place to start is looking at the doctrine of the “witness of God” made up of two .One seen the temporal the other not seen the eternal
A picture of the Father and Son working together in perfect harmony  and mutual submission . They working as one bring us the peace of His understanding. .  that which can work in mankind. 
No father no son, no son no father .
1 John 2:22 Who is a liar but he that denieth that Jesus is the Christ? He is antichrist, that denieth the Father and the Son. Whosoever denieth the Son, the same hath not the Father: he that acknowledgeth the Son hath the Father also.
It would appear the word “two” is used to represent the one perfect witness of God not seen, the greater witness that works in mankind seen.
The law of God’s good news is the whole bible .Without it all perishes and with it some also do.
Romans 2:12 For as many as have sinned 
without law shall also perish 
without law: and as many as have sinned 
in the law shall be judged 
by the law
Moses is used to signify the letter (scripture) of law pronouncing all are dead in trespasses and sin, while the prophets beginning with Elijah. . the law of faith the unseen resurrection power.
Romans 7:6But now we are delivered 
from the law, that 
being "dead wherein" we 
were held; that we should serve in 
newness of 
spirit, and not in the 
oldness of the letter.
Luke 1:17 And he shall go before him in the
 spirit and
 power of 
Elias, to turn the hearts of the fathers to the children, and the disobedient to the wisdom of the just; 
to make ready a people prepared for the
 Lord.
The unseen power signified by the prophets who were moved by the power to proclaim his living abiding word.  
The law of God (scripture as 
it is written ) the visible witness of God (signified by Moses) it is coupled with the unseen witness of faith or labor of God's Love . (signified by the word of God spoken through the prophet Elias. So then it is shown in two ways . . . to the law and or with the prophets, or to Moses and and Elijah. Those two laws working together form one new perfect law or complete law. (Psalm 19 ) Apart from each other there can be no grace. Resulting in death the letter
Moses and the prophets or or saying the same thing. .  Moses and Elias .With Elias representing all the prophets again all together make up the one perfect witness of God the perfect law (old and new testement) .
Luke 16:31 And he said unto him, If they hear not 
Moses and the prophets, neither will they be persuaded, though 
one rose from the 
dead.
Moses and the prophets, (the witness of God)The witness of two.
Luke 24:44 And he said unto them, These are the words which I spake unto you, while I was yet with you, that all things must be fulfilled, which were 
written in the law of Moses, and in the prophets, and in the psalms, 
concerning me
Again two to represent the perfect or complete.
Matthew 17:3 And, behold, there appeared unto them 
Moses and Elias talking with him
1 John 5:9 If we receive the 
witness of men, the witness of God is 
greater: for 
this is the witness of God which 
he hath t
estified of his Son.
In that way we acknowledge it is Christ in us working to both will give us a desire and empower us to do the good pleasure of Him who does make our hearts soft . He completes the whole circuit the perfect . No short circuits with Him . We have his promise in Philippians 1:6 if he has begun the good work of salvation in us he will finish it as we work with him making our burden lighter. .
The gospel the perfect law  as 
it is written in the Psalm.
Psalm 19: 6-11 His going forth is from the 
end of the heaven, and 
his circuit unto the 
ends of it: and there is nothing hid from the heat thereof.The
 law of the Lord is perfect, 
converting the soul: the testimony of the Lord is sure, 
making wise the simple.The statutes of the Lord are right, r
ejoicing the heart: the commandment of the Lord is pure, 
enlightening the eyes. The fear of the Lord is clean, 
enduring for ever: the judgments of the Lord 
are true and righteous altogether. More to be desired are they than gold, yea, than much fine gold: sweeter also than honey and the honeycomb. Moreover by
 them is thy servant 
warned: and in keeping of them there is 
great reward.