"There is no (other) god except God and Muhammad is His messenger". This declaration of faith is called the Shahada, a simple formula which all the faithful pronounce. In Arabic, the first part is la ilaha illa'Llah - 'there is no god except God'; ilaha (god) can refer to anything which we may be tempted to put in place of God -- wealth, power, and the like. Then comes illa'Llah:' 'except God', the source of all Creation. The second part of the Shahada is Muhammadun rasulu'Llah: 'Muhammad is the messenger of God'. God's message of guidance has come through the Prophets from Adam through to Muhammed.
The first pillar of Islam is that a Muslim believes and declares his faith by saying the Shahadah (lit. 'witness'), also known as the Kalimah:
La ilaha ila Allah; Muhammadur-rasul Allah.
'There is no god but Allah; Muhammad is the Messenger of Allah'.
This declaration contains two parts. The first part refers to God Almighty, the Creator of everything, the Lord of the Worlds; the second part refers to the Messenger Muhammad (pbuh) a prophet and a human being, who received the revelation through the Archangel Gabriel, and taught it to mankind.
The Prophet, pbuh, said: 'The right of God upon His servants
is that they worship and serve Him alone, and make none a
god beside Him; and the right of servants upon God is that He
does not punish those who do not make anything a god beside
Him.' (Authenticated by: Bukhari & Muslim)
The requirements of this Testimony is the submission and declaration that Allah is the true God, and that all other deities are False, and are not capable of either harming or benefiting, nor do they deserve to be worshipped.
Allah is also the Ruler who has a free hand in the disposal of the affairs of the universe. People must rule by His laws and commands. It is to the Holy Quran to whom men should refer their disputes and affairs. Any judicial decision other than Allah's, is a decision based on ignorance or a pre-Islamic era, which entails injustice and deviation. All legitimate rites of worship must be dedicated to Allah alone.
Among other requirements of the Testimony of Faith is that no one should bow down, or lower his head humbly to anyone, nor supplicate to another human asking him to fulfil his needs, for only Allah is capable of fulfilling man's needs. This rejection must extend to all other conceptions, superstitions, ideologies, ways of life, and authority figures that claim supreme devotion, loyalty, trust, love, obedience or worship. This entails, for example, the rejection of belief in such common things as astrology, palm reading, good luck charms, fortune-telling and psychic readings. A Muslim prays directly and exclusively to Allah.
As for the requirements of the Testimony: 'Muhammad is the Messenger of Allah', it entails recognition of Muhammad as the true Messenger of Allah. This Testimony also attests to his veracity, trustworthiness and infallibility in everything and what he related about Allah, the Exalted, about the past, the future, and the unseen world, as everything he related is only revelation from Allah.
It is obligatory to obey his commands and to refrain from his prohibitions because obeying him is in fact obeying Allah's command. The Prophet, peace be upon him, is the one commissioned by Allah to convey His message, laws, and commands. Therefore, it is not permissible to disobey the Messenger, peace be upon him, for disobeying him means disobeying Allah.