His word does not return void ש
The shin ש is drawn with a vav descending down the right side (God speaking into the void) and two zayins ז returning. God's word does not return void, but brings back an increase. 
John recognizes it as the Spirit in the word for heaven shamayim שמים.  It is likely he obtained this from the formation of the word 'heavens' in Ge 1:2 where the Spirit ש moved on the face of the waters 'mayim' מים.
As a metaphor it can be expressed as a marriage (the increase), as in the name Yeshua (Jesus) which is Yahweh with a marriage ש in his heart, fulfilling the prophecy of "God with us".
Tradition now says that it can be pronounced as a 'sh' or a 's'. The word shibboleth means an ear of corn, or stream. If it is pronounced as a 's' it sounds like Sibboleth, which means a single grain. The difference is the difference between life and death.  It is a question of what do you say of Christ, who is he? Is he the single corn that died, or is he the ear of corn which is fruitful in resurrection?
Why would such a tradition arise? Could it be that men who did not want to proclaim Christ as the Messiah choose to say Sibboleth?
The word 'name' meaning reputation is shem שם. God's reputation is based on him completing ם (obtaining a people) the fruitfulness of his word ש.
One of the primary metaphors of the aleph was separation. 'Lift up' sa שא is what happens to the bride as she is raptured and separated from the earth.
The gift 'shay' שי to the bride ש is a new life י.
Next: He completed his work ת
- Isa 55:11 So shall my word be that goeth forth out of my mouth: it shall not return unto me void, but it shall accomplish that which I please, and it shall prosper [in the thing] whereto I sent it.
- 1Jo 5:7 For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one.
- Jud 12:6 Then said they unto him, Say now Shibboleth: and he said Sibboleth: for he could not frame to pronounce [it] right. Then they took him, and slew him at the passages of Jordan: and there fell at that time of the Ephraimites forty and two thousand.