What is the ruling on the statement that "La ilaha illa Allah" begins with realizing "there is no deity worthy of worship except Allah" and its highest rank is "there is nothing truly existent except Allah"?

Negating the existence of anything other than God is not part of Tawhid (monotheism). Allah Almighty commanded us to reflect upon His cosmic signs, which demonstrate His greatness and power. He forbade us from exalting and worshipping created beings, but He did not ask us to believe in their non-existence. What is required is to achieve the worship of Allah alone and to disbelieve in what is worshipped besides Him, as stated in His Almighty saying: "So whoever disbelieves in Taghut and believes in Allah has grasped the most trustworthy handhold," and the Prophet's (peace be upon him) saying: "Whoever says 'there is no god but Allah' and disbelieves in what is worshipped besides Allah, his wealth and blood are inviolable, and his reckoning is with Allah." The aforementioned statement resembles the disbelief-laden doctrine of Wahdat al-Wujud (unity of existence).