[Iris Alantiel]

I always attributed Aragorn's pause to the fact that Theoden speaks of the "victorious" dead. At this point, Sauron still reigns and Aragorn does not know what has become of Frodo. Since there is still considerable potential for Sauron to win the war, then, I always imagined Aragorn was reflecting on whether the dead could really be called "victorious" yet and what responsibility he had for making sure they really were victorious (which would not be the case if they died fighting for Rohan only to have Sauron defeat the race of Men at Pelennor). I rather imagine him making a silent vow renewing his commitment to the war, something to the effect that he would honour those who died at Helm's Deep (perhaps especially Haldir and anyone else he might have known who died) by making sure Sauron was defeated and their deaths were not in vain.