My preferred approach is something like the following.

The abstract is written for the experts. You don't need to say anything about originality, how clever you are, and how important your results are. Just tell what you've done.

The introduction should put your work in context. What has been done before, and what you have done to advance knowledge.

The experts will be happy with just that.

But then, as people discussed below, there are the reviewers.

And, more importantly, there are the intended readers that are not expert.

Mostly, these readers are PhD students, that is, the next generation of researchers. Nobody mentioned this in the discussions in this thread.

But these readers may also include people from neighbouring fields whose work either (1) could benefit from your work, or (2) could potentially contribute to your work. Such people must be addressed too.

At the end of the introduction, however you chose to write it, it is nice to have a quick summary of what you think your contributions are.

(Anecdote. Recently I was in a position to help the authors of a paper, as a journal editor, to add more to what they thought their contributions were. They didn't realize that there was something significant in the technical development that was worth adding to the introduction.)

Also, don't conflate writing a conference paper with writing a journal paper, or a grant application or a job application.

The last two require a completely different approach, and I don't have any good advice to give regarding them.