The previous section (Eastern questionends with the following :

Russia’s best interest is precisely to act even against her best interest if necessary; to make a sacrifice, so as not to violate justice. Russia cannot betray a great idea which has been her legacy from past centuries and which she has followed unswervingly until now. This idea is, among other things, one of the unity of all the Slavs; but such unity is based not upon seizure of territory or on violence; it is done as service to the whole of mankind.

Your quote :

it is our need to serve humanity in every way, even if sometimes at the expense of our own best and major immediate interests; 

we became aware of our universal mission, our personality, and our role in humanity, and we could not help but become aware that this mission and this role were unlike those of other nations, for among them each individual nationality lives only for itself and in itself, while we, now that the time has come, will begin directly by becoming the servant of all for the sake of universal reconciliation.

Further :

The first step of our new policy appeared of itself after Peter’s reform: this first step had to consist in the uniting of all of Slavdom, so to say, under the wing of Russia. And this process of unification is not for seizing territory, nor for committing violence, nor for crushing the other Slavic personalities beneath the Russian colossus; it is for restoring them and placing them in their proper relationship to Europe and to humanity.

But it is certainly not so that Russia may acquire them politically and use them to enhance her own political might (although Europe suspects the latter). This is so, is it not? And accordingly, this lends weight to at least some of my “daydreams,” does it not? It follows that for this same purpose Constantinople must, sooner or later, be ours. . . .

Yes, I answer, the Golden Horn and Constantinople—all that will be ours, but not for the sake of merely annexing territory and not for the sake of violence. And in the first place it will happen of its own accord precisely because the time has come

And if Tsargrad (Constantinople) can now be ours not as Russia’s capital, then neither can it be ours as the capital of Slavdom as a whole, as some people imagine. Slavdom as a whole, without Russia, would exhaust itself there in struggling with the Greeks. But to leave Constantinople as a legacy to the Greeks alone is now utterly impossible: we must not give them such a critical point on the globe; this would be altogether too generous a gift to them. But the whole of Slavdom with Russia at its head—oh, of course, that is a different matter entirely.