This entire post is simply a translation from Siftei Chaim vol. 3 pg. 284 by Rabbi Chaim Freidlander
And when the builders laid the foundation of the Temple of hashem, they set the priests in their clothing with trumpets, and the Levites in their clothing with cymbals, to praise hashemin the manner of David, the king of Israel. And they responded with Hallel in praising and giving thanks to hashem, because the foundation of the House of hashemwas laid. But many of the priests and the Levites and the chiefs of the father’s houses, old men who had seen the first Temple; when the foundation of this house was laid before their eyes, wept with a loud voice; but many shouted aloud for joy. So much that people could not distinguish the sound of joy from the sound of the weeping of the people; for the people shouted with a loud shout, and the sound was heard from afar.
Ezra, Chapter 3 verses 10 – 13
At the establishment of the second Temple there was a very strange phenomena. On the one hand the youth who did not remember or recognize the first Temple in its glory, for seventy years had already passed since its destruction, blasted with joy the sounds of the terua (Shofar) upon the establishment of the House of hashem. On the other hand there stood the elders, who had merited to see the first Temple in its glory. Not only did the elders not participate in the celebration, rather they cried out in full voice, until their cries drowned out the sounds of the celebration.
The structure of the second Temple was almost the same as the first Temple. There were only five things missing in the second Temple – and one of them was the indwelling of the divine presence! This is the essential difference between the time of the first Temple and the time of the second Temple. Those who had meritted seeing and understanding the indwelling of the divine presence in the first Temple, they understand well the meaning of the destruction. Such that even if they in fact merited the building of a second Temple, but it was missing the divine presence, they none the less continued to mourn the destruction of the first Temple for that lacking. But those who never merited to witness the first Temple, could not begin to understand the tears, once they had merited to build the second Temple.
We, because of our great sins, mourn the loss of two Temples: the first and the second. However, it is difficult to cry or to truly understand the meaning of the destruction. We do not understand at all what was lost, we lack the knowledge and understanding of the regular situation of the Jewish People in their glory, for we never saw or understood it. The opposite is true, amongst our sins is that we feel that things are good, despite all of the suffering that surrounds us, as though we are not missing anything – not physically nor spiritually. This feeling is what prevents us from truly mourning the destruction as we ought to, since we can not really feel what is missing. Therefore we are obligated to learn and understand the inner meaning of the destruction, to feel and know the lowliness of our situation and our station from the destruction until now.