Seal in this context does not mean final. It means that he is representative of prophethood or his 'signature'( not literal) is enough to issue decrees.Qalima-e-Shahadah does not intricately word "Finality of Prophethood," yes. It is the basis of becoming Muslim, and as we become Muslim our belief in the word of Allah Subhanaho Wata'aalah is based on our belief in the Holy Qur'an as HIS word. You can dodge, in your utter ignorance and illiteracy, from the Qalima-e-Shahadah all you want. But what you cannot dogde is the Holy Qur'an.
Judging by your hostility, it seems as though you are qadiyani. Am I correct in assuming this? You do not need to be hostile, I am defending my faith in Allah Subhanaho Wata'aalah. I invite you to have a discussion on this subject, without any hostility from me to you. As a Muslim, I give you my word. And I suggest this, so that we discuss the matter, with our intellect, and not hotheads.
Sorry that his a very arrogant definition of Kafir. You cannot say that a kafir worships false gods. That's reverse blasphemy.A Kafir is someone who rejects Islam for their own belief in false gods. But these qadiyanis are something else, they claim to be Muslim, yet the commit Kufr which is at the very core of a Muslim's belief. Claiming a man to be the Prophet of Allah, after Nabi Muhammad Alaihi Salaat-u-Wassalam. Now that is pure sinister, devious and evil.
You have to accept that there is a world outside of your religion (any religion) and this diversity is important to understand the world around us.