Islam is about giving Thanks.
Of course, who deserves most and all thanks all the time, and for everything good that every comes our way, but Allah?
So, there is no better way to say "Thank You!" to Allah than Alhamdu Lillah, which for that very reason is also the best Du'a you can make.
And in Islam, Hadith tells us, the way to Thanking Allah passes through the intermediary stage of Thanking People.
And Hadith Sharif also tells us that there is no better way to thank people than to say to them: Jazaakallah!
At the same, we are English-speaking people, surrounded by a certain cultural environment, and there is nothing wrong in our trying to take some time and make a special effort to find some appropriate "Extra Words" in English to move the conversation forward, such as, for example:
- I really appreciate the effort you made to send me this invitation, Dr. so-and-so. I will check my schedule and see what I can do. And let you know.
- Thank you so much, Dr. so-and-so, for including me in this list of special invitees to the Arabic Class. I will do my best to take advantage of this opportunity that does not come along every day.
- And so on.
This is called Everyday Norms of Civilized Behavior. And Islam is all about behaving in the most Civilized Way toward those you know as well as toward those you don't know.
That is why, and that is how, Islam spread like Wildfire. People just fell in love with the way Muslims conducted themselves.