I have got the first revision of my paper from a journal in Elsiver. Despite, all 3 reviewers' comment are very positive and accepted the paper the editor is so tough. He is questioning the originality of the proposed method and also saying the paper is not very much in the scope of journal. If so, why did you hand it to reviewers?!!! Any idea to answer him/her?
I really think that you are looking at things the wrong way. The key fact -- your paper has not been rejected! -- was left unsaid in the question itself but got pulled out of you in the comments. What makes an editor "tough" or not has virtually nothing to do with the words he uses to describe your paper. A truly tough editor will reject your paper based on flaws that you disagree with or feel are very minor. A moderately tough editor will require drastic revisions (perhaps in multiple rounds) that take up your time and delay the acceptance and/or publication of your paper. That's about it.
You don't sound very well informed about the process. What you received were not "revisions" but "reports" or "reviews". Moreover it is not for a referee/reviewer to accept or reject a paper. That is up to the editorial board. Rather, a referee/reviewer should recommend acceptance or rejection -- I have just learned that in some journals and fields this recommendation is made confidentially to the editor; that is certainly not the case in mathematics, and I think it is a poor idea to keep this information from the author, but let me not digress -- and then the majority of the report / review should contain support for that recommendation. (So if a report is thorough and well written, the author should be able guess immediately and accurately what the recommendation will be. Thus hiding the recommendation seems pointless.) A report which just says "Accept" is worthless, and many editors would just discard it.
He is questioning the originality of the proposed method and also saying the paper is not very much in the scope of journal. If so, why did you hand it to reviewers?!!!
The alternative would be to reject the paper immediately. Obviously the editor's reservations about the paper did not rise to that level. It doesn't make much sense that you are complaining about that.
Any idea to answer him/her?
Yes. Your answer should come in the form of a revised paper that at least addresses all of his suggestions (which, by the way, can probably be addressed with relatively superficial changes, mostly to the introduction and the conclusion, if present). If you don't understand a suggestion, you can write for clarification, but I would be careful about that since the editor's impression of your willingness and ability to make the changes is part of his assessment of the paper. If you are really new at this (it sounds like you are, honestly) then I highly recommend that you consult at least one advisor, mentor or senior colleague about how to perform these revisions.
The one worrisome part of what the editor said is
The present form does not have sufficient results to justify the novelty of a high quality journal paper.
If the editor (or the editorial board) really feels that the results are not strong enough to merit publication in that journal, they can and probably will reject your paper, no matter what any number of referees says. I have seen this happen as a referee: I wrote a quite positive report, but the editor (a former mentor of mine) called me up on the phone to tell me that the paper was not going to be accepted. However, it is a bit strange to say that while still asking for a revision. Reading between the lines, the implication is that he finds the work of the paper a bit borderline, so he really wants the presentation to be otherwise impeccable.
Of course you always have the option of not revising the paper, and starting fresh with a different journal. But I don't recommend that: when you are asked to revise, revise. The vast majority of time, that means "accepted with some penance".
In many reviews in a variety of fields, including the Elsevier life science journals for which I've reviewed (maybe a half dozen to a dozen), the authors are not made privy to the the recommendations of the reviewers. Reviewers are specifically asked to refrain from including any direct recommendations for acceptance or rejection in their author comments.
In an environment where there's just so many pages that can be printed, the bar can be pretty high, and only the top of the top might make it to print in very competitive journals. There are often reviewer assigned scores that you never see, like "novelty", and "importance"
Another possibility is that the editor feels that while the paper might be received well by people in your field, but not to the broader audience of a widely read journal. Often reviewers must answer a question about their opinions on the appropriateness of a paper for that particular journal. It sounds like this may well be the case here, and your reviewers might have given you mediocre scores along these lines, even though their written comments on your work were encouraging.
Also, many reviewers will try to put as positive a tone as possible on a review, particularly for young investigators. The risk is that a young investigator might not have developed the skill to read between the lines.