To add to what has already been written above.
There are three aspects of Deen. Iman, Islam and Ihsan. These are studied as 'Aqeedah, Fiqh and Tazkiyyah/Tassuwwuf/Jihad … Note: that Shahadah is not in the 'aqeedah teachings, rather it is in the Fiqh. The simplest breakdown of Fiqh is Shahadah, Salat, Zakat, Sayam, Hajj.
Building on Shahadah leads to Dawah, Salat to other forms of Dzikr, Zakat to Sadaqah, Sayam to Nufli Sayam and Forms of dzikr/khalwa and Hajj leads to preparation to be independent of domicile or preparedness for hijra and undertaking of Ummrah, etc.
The basic ones are required the other versions are by choice and level of iman.
The 'aqeedah needs to be in tact before one can consider himself/herself a Muslim.
So the fundamental difference between 'aqeedah and fiqh is that 'aqeedah tells us how we should “understand” and “accept” in our hearts, and fiqh teaches us how we should “perform” rites and rituals.
Shahadah therefore is a ritual. Declaration is an ACT it is not a condition of the heart. To be a Muslim one must believe it in the heart. Once taking Shahadah then the belief of a person becomes a public affair. The ummah then has responsibilities over that person and that person over the ummah, because that person officially joins the ummah upon Shahadah.
Before Shahadah a person may perform wudu, salat and other Islamic practices without other obligations. Also, before Shahadah the person may stop doing Islamic practices if they so choose without state getting involved or fear of being branded murtad, etc.
**For Muslims we should encourage people who are interested in Islam to practice Islamic behaviour and attitude without stressing upon them to take Shahadah.
**Notice how the order is Muslim, Mo’min, Muhsin. A person is only considered a Mo’min when all of the matters of belief are reflected in their actions. A Muslim is the one who aspires to meet all actions to conform with the beliefs. A Muhsin is one who strives to rid any imperfections in actions and belief and make them conform with one another.
**Shahadah represents the vocalisation of belief not the belief itself.
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Note: For children the rituals will tend to precede the beliefs, whereas for new Muslims who choose to become Muslim need to be choosing Islam based on the beliefs, but then practice just like children would and then make Declaration.
