מעם לועז (Shemot 3, p. 965, quoting Rikkanti, Ramban, Rabbeinu Bechaye, and Toldot Yitzchak) explains the reason for the Shulchan (Table) and the Lechem HaPanim (Bread of Presence). After the six days of Creation, Hashem chose not to perform open miracles but to operate within the natural order. Blessing does not rest on nothingness; there must be a vessel to receive it. This is illustrated by the story of Elisha and the widow's oil, where the blessing multiplied only once a small amount was present.
Therefore, Hashem commanded the making of the Shulchan and the Lechem HaPanim, so there would always be a preparation for heavenly abundance. When the Beit HaMikdash stood, the Shulchan with the Lechem HaPanim was a sign of Hashem's love for Israel, as sustenance for the world descended upon it. The Shulchan was never to be empty, even for a moment, as blessing does not rest in an empty place. Similarly, when reciting the blessing over bread or Birkat HaMazon, one should have bread on the table, and words of Torah should be spoken at the table to make it like the Shulchan before Hashem. Additionally, one should have compassion for the poor, as such a table is accompanied by two angels who bless the host in this world and the next.
