This work by St. Ambrose discusses the comparison between the manna from heaven and the true body of Christ, asserting that while the former is a mere shadow, the latter represents the ultimate truth and sustenance. It highlights the impermanence of manna, which is subject to corruption, versus the eternal and incorruptible nature of Christ's flesh. The text also references biblical examples to reinforce the idea that the true essence of faith transcends mere appearances, encouraging believers to recognize the profound reality of Christ's presence in the Eucharist.