By ‘Sunnah’, which means ‘the tradition’, what is meant is the general tradition of all the prophets and messengers from Adam, the First to Muhammad, the Last (peace be upon them all). This tradition is focussed on Towhid (monotheism, the One-ness of Allah). It is also refers to the specific tradition of the Last prophet as his alloted time lasts till the Last Day. In this sense, it is a short hand for us to follow what has been revealed via the Qur’an (Allah’s revelation to the prophet- Most Exalted be Allah, The Lord of All that exists) and the Sunnah (the traditions of the Last prophet).
By ‘Jamaah’, what is meant is generally the ijma (consensus) of the community of believers, which is a reference to the early community around the prophet (peace be to him) that included the first three generations. Their understanding is critical – even now – because they were the closest to his way (his Sunnah) and lived it after he died. The superiority of their perspectives that should never be overlooked is vouched for and supported by authentic hadiths. Specifically, however, ‘Jamaah’ is a reference to the necessity to imbibe the ‘Heart-Action’ (one of the parts of faith outlined previously) without which whatever knowledge and whatever action we possess or demonstrate is ultimately meaningless.
“And hold firmly to the rope of Allah all together and do not become divided. And remember the favor of Allah upon you – when you were enemies and He brought your hearts together and you became, by His favor, brothers. And you were on the edge of a pit of the Fire, and He saved you from it. Thus does Allah make clear to you His verses that you may be guided.”
(Qur’an, Surah Al-Imran 3:103 – My emphasis, bold and italic)
So here we have a direct connection between loyalty, obedience, practice and necessity for Allah’s ‘rope’ or His Way (Qur’an and Sunnah) and our hearts (hence, Heart-Action).
This is why this topic of aqeedah is critical to first know and then apply.