The short answer, is that he is very much with us - in the Eucharist and the Church. Unfortunately, that answer does not suffice for most skeptics, as I know very well from the time when I was a skeptic myself.
The long answer, is that the Old Testament covered a totally different era in the economy of salvation. Before Christ, there was no direct mediator between God and man. Although God’s presence was manifested in the Temple, he did not “communicate”, so to speak, through the Temple. This, rather, was done only occasionally, through the prophets. Although this type of direct revalation may sound more " involved" to skeptics, in reality it was not enough for man to be saved by. Christ’s coming instituted a totally different era. The barriers between God and man were broken down. God literally came into the world himself, as one of our own kind, opening up the path of “revelation” to all mankind, not just a select few. And he promised to make us his new Holy Temple, through the institution of the Eucharist. And after comitting the ultimate act that was necessary for the salvation of man - his own self-sacrifice, the ultimate sin offering - he bestowed his own Spirit upon the Church, making the Church his new prophet, in addition to making the Church’s Body the new Temple.
Hopefully I’ve explained it adequately enough - it’s all very complicated theology that’s all very easy to get lost in. I don’t pretend to understand it fully myself.