Commentary for Zechariah 14:9

shall the Lord be one For all the nations shall abandon their vanities and acknowledge Him, that He is one, and [that] no strange deity is with Him.

And the Lord shall become King over all the earth – this is the meaning of the metaphor of the water, that the whole world will recognize the Lord’s sovereignty and unity. Until now there were nations which did not believe in His unity, and said that there were two or more points of origin. Then ‘the Lord will be one,’ and the nations who acknowledged the unity of the Lord but combined another agent with His guiding of the world, or with His name, memory or nobility, etc…Then His name will also be one, because everyone will believe in the true unity, His special providence and guidance and his sovereignty. So too in the future the four-lettered name will be read as it is written, because the use of appellations is due to the divisions between lovingkindness, mercy and the like in His guidance of the world. In the future there will be one simple mode of guidance:

And the Lord shall become King - When the nations who come to Jerusalem see the wonders mentioned here, they will recognize that the Lord reigns over all the earth and exerts His providence on the lower world. He does with them as he pleases, and nature is transformed to do the will of those who fear Him, because everything is the work of His hands:

and His name one That His name shall be mentioned by everyone.