There is no god but Allah” is the best speech, and it is the basis of religion and the foundation of the religion, and it is with which the Messengers - may blessings and peace be upon them - began with their people.by saying: Say there is no god but Allah, you will be successful.The Almighty says:
وَمَا أَرْسَلْنَا مِنْ قَبْلِكَ مِنْ رَسُولٍ إِلا نُوحِي إِلَيْهِ أَنَّهُ لا إِلَهَ إِلا أَنَا فَاعْبُدُونِ [الأنبياء:25]
And We sent not before you any messenger except that We revealed to him that, "There is no deity except Me, so worship Me.[Anbiyah 25].
It is the basis of religion and denomination, and the one who says it must know its meaning, for it means that there is no deity in truth but Allah, and it has conditions, which are: knowledge of its meaning and certainty, not doubting its validity, devotion to Allah in that alone, truthfulness in his heart and tongue, and love for what it indicates of sincerity.accepting that, submitting to Him, uniting Him, rejecting polytheism with Him and disavowing the worship of others and the belief that it is false.