It is narrated on the authority of Caliph Uthman that the Messenger of Allah ﷺsaid: He who died knowing fully well that there is no God but Allah entered Paradise.
(Sahih Muslim)
Belief without action is tantamount to no belief as belief entails action in accordance with the belief. That is why some persons ask whether it is enough for a man that he should recite kalimah in order to enter the Paradise.
A close analysis of the hadīth reveals that mere expression of these words does not suffice. It implies that he who sincerely professes that there is no God but Allah deserves admittance to the Paradise. And this in turn entails heavy responsibilities; for assertion of a statement demands action in strict accordance with the assertion. It means that the man is declaring in unequivocal terms that he believes in one God, and does not associate any other deity with Him, whether those made of stone, clay or any other material or heavenly bodies or human beings. Those who know fully well the taste of the kalimah cannot stand passive.
The man who negates the existence of all false gods and affirms the existence of One True God in fact professes that he would submit to His command alone and nothing else except that which has been vouchsafed to him by the Prophet. Thus, the affirmation of this simple truth covers all the responsibilities, obligations and duties which fall upon the shoulders of a man after accepting Him as the sole object of worship.