God knew Moses was perfect for the job

And the LORD said unto Moses,     When thou goest to return into Egypt, see that thou do all those wonders before Pharaoh,
                                                     which I have put in thine hand: but I will harden his heart,  that he shall not
                                                     let the people go.                        Exodus 4:21
                                                                           How? (some thoughts on this matter)

1.   Moses was a shepherd.     

                                               reference  Genesis 46:33   And it shall come to pass, when Pharaoh shall call you, and shall say, What is your occupation?
                                                                  Genesis 46:34   That ye shall say, Thy servants' trade hath been about cattle from our youth even until now, both we,
                                                                                                                               and also our fathers: that ye may dwell in the land of Goshen; for every shepherd is an abomination
                                                                                                                               unto the Egyptians.                                                                            

Moses the shepherd by the burning bush
 Moses the shepherd by the burning bush
by Gerard Jollain French 1670

2.   Moses used a shepherd's tool (his rod) to persuade the Pharaoh    (it became an arsenal)
    
                                      reference  Exodus 4:2            And the LORD said unto him, "What is that in thine hand?" And he said, "A rod"
                                                                                          Exodus 4:17        "And thou shalt take this rod in thine hand, wherewith thou shalt do signs."

The Staff Transformed to Serpent
Moses and Aaron before the Pharaoh
by Benjamin West American 1738-1820

Moses and Aaron before Pharaoh
Moses and Aaron and the Arsenal
by Nicolas Poussin French 1594-1665

Moses and Aaron before the Pharaoh
Moses and Aaron before the Pharaoh
by Gustave Dore French 1865

Moses and Aaron displaying their Arsonal
Moses and Aaron displaying their Arsonal
by unknown to me

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3.   Two men, an 80 year old shepherd who couldn't speak well, the other an 83 year old Hebrew slave

                                                             reference  Exodus 4:10     And Moses said ....... I am not eloquent, ...... but I am slow of speech, and of a slow tongue.   
                                                                                Exodus 7:7       And Moses was fourscore years old, and Aaron fourscore and three years old, when they spake unto Pharaoh 
                                                                                                                                                                                    

Knowing this ...  sending Moses in itself would harden Pharaoh's heart

Adding to that                                                                        

4.   Bringing the Hebrew slave elders (old people) with him.  (seems like rubbing it in from Pharaoh's perspective) 

                                     reference  Exodus 3:18  (previous page)

5.   Presenting the Pharaoh with a Hebrew slave's God that is superior to his gods or him.     
                                                                                          (Pharaoh's ego is at work I would say) 

                                               reference  Exodus 5:2  And Pharaoh said, Who is the LORD, that I should obey his voice to let Israel go?

                                                                                                                       I know not the LORD,  neither will I let Israel go.

 

Pharaoh in Control with a Hardened Heart
Pharaoh in Control with a Hardened Heart
by James Tissot French 1836-1902

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6.   The arragance to approach the Pharaoh demanding release of his work force.

                                     reference  Exodus 5:4-23  Pharaoh's response    (the results of the meeting)
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Pharaoh and His Slain First Born
Pharaoh and His Slain First  Born
by AlmaTadema Dutch 1836-1912

7.  The Ultimatum    if - then

                           reference  Exodus 4:22  And thou shalt say unto Pharaoh, Thus saith the LORD,
                                                                        Israel is my son, even my firstborn: 
                                                              Exodus 4:23  And I say unto thee, Let my son go, that he may serve me:
                                                                        and if thou refuse to let him go, behold, I will slay thy son,
                                                                        even thy firstborn.