What does Oliver Wendell Holmes, Jr. mean by 'continuity with the past is only a necessity'?

Question

_{Preface: I first encountered the bolded on p 220, Is Eating People Wrong? Great Legal Cases and How They Shaped the World (2011) by Allan C. Hutchinson.
Source: p 185, The Essential Holmes: Selections from [...] Oliver Wendell Holmes, Jr., edited by Richard Posner.
Original Source: Law in Science and Science in Law, 12 Harvard Law Review 443 (1899).}

     This process of historical explanation has been applied to the matter of our profession, especially Of recent years, with great success, and with so much eagerness, and with such a feeling that When you had true historic dogma you had the last word not only in the present but for the immediate future, that I have felt warranted heretofore in throwing out the caution that continuity with the past is only a necessity and not a duty. As soon as a legislature is able to imagine abolishing the requirement of a consideration for a simple contract, it is at perfect liberty to abolish it, if it thinks it wise to do so, without the slightest regard to continuity with the past. The continuity simply limits the possibilities of our imagination, and settles the terms in which we shall be compelled to think.

I do not comprehend the bolded: How is continuity even a necessity for the law, much less a duty? As Holmes himself states in the last sentence above, a legislature can ignore the past and create something entirely new; I also know that some activist judges can do so.

Answer 1

I read his point as being that continuity in law may be a necessity, but it is not a duty of those who are interpreting the law to overuse continuity: black-letter law and precedent should be followed but also understood.

Thus when the law exists it should not be changed by a judge bound to follow precedent, but when there is a close question, the judge or advocate should step beyond the necessity of merely accepting precedent as showing the right result by analogy--he should understand that competing social ideas are at work and address that conflict directly in his thinking and his decision.

Page 460 of the article has a great explanation:

My object is not so much to point out what seems to me to be fallacies in particular cases as to enforce by various examples and in various applications the need of scrutinizing the reasons for the rules which we follow, and of not being contented with hollow forms of words merely because they have been used very often and have been repeated from one end of the union to the other. We must think things not words, or at least we must constantly translate our words into the facts for which they stand, if we are to keep to the real and the true. I sometimes tell students that the law schools pursue an inspirational combined with a logical method, that is, the postulates are taken for granted upon authority without inquiry into their worth, and then logic is used as the only tool to develop the results. It is a necessary method for the purpose of teaching dogma. But inasmuch as the real justification of a rule of law, if there be one, is that it helps to bring about a social end which we desire, it is no less necessary that those who make and develop the law should have those ends articulately in their minds. I do not expect or think it desirable that the judges should undertake to renovate the law. That is not their province. Indeed precisely because I believe that the world would be just as well off if it lived under laws that differed from ours in many ways, and because I believe that the claim of our especial code to respect is simply that it exists, that it is the one to which we have become accustomed, and not that it represents an eternal principle, I am slow to consent to overruling a precedent, and think that our most important duty is to see that the judicial duel shall be fought out in the accustomed way. But I think it most important to remember whenever a doubtful case arises, with certain analogies on one side and other analogies on the other, that what really is before us is a conflict between two social desires, each of which seeks to extend its dominion over the case, and which cannot both have their way.

(Thanks to cpast for the link)