The following passage is from “The Way of the Spirit: Reflections on Life in God” by Archimandrite Aimilianos of Simonopetra (Indiktos: Athens 2009), chapter six on Awaiting Pentecost.
He was seen by them for forty days, speaking to them about the kingdom of God (Acts 1.3). Here we see two forms of Christ’s manifestation, which are of great significance: the fact that He was seen, and that this was an event which unfolded over a period of forty days.
These are the ultimate self-revelations of Christ. They are the most dynamic manifestations of His life. This is now the definitive way that He expresses Himself, and it is not going to change. Everything transient is here put aside, and is replaced by that which abides permanently, eternally. At the same time, that which is eternal is available to all. “Even if your heart has been hardened by sin; even if you’re spiritually blind; worse than the Israelites in the desert, nevertheless, I give you the means to understand these things.”
Let these truths be deeply felt by us, for they are the mystery of the Church, which is the experience of Christ, the eternal Christ, extended throughout time and existing unfailingly in eternity.
He was seen by them for forty days, speaking to them about the kingdom of God. Why does it say for forty days? The number forty had great significance for the Jews, and occurs constantly throughout the Old Testament. The flood continued forty days and nights upon the earth (Gen 7.4, 17). Isaac was forty when he married Rebecca (Gen 25.20; cf. 26.34). David reigned for forty years (2 Kg 5.4; 3 Kg 2.11), as did Solomon, his son (3 Kg 11.42). Elijah received sustenance from an angel, and went in the strength of that food for forty days and nights (3 Kg 19.8). The manna from heaven was eaten for forty years (Ex 16.35). The people wandered for forty years in the desert (Deut 29.4; Amos 2.10). Moses remained on Sinai for forty days and forty nights, speaking with God (Ex 24.18, 34.28; cf. Deut 9.9).
The number forty is a symbol of completion. It signifies a fullness which admits of no further perfection. It nearly always refers to the advent of new life, of a new creation. The number seven is also an expression of completeness: God created the world in seven days (Gen 2.2-3), and thus the number seven marks an earthly, cosmic perfection. But the number forty pertains directly to God, to the acquisition of God, to participation in His life. This is why there is no “forty-first” day.
In order for Moses to see God, he had to fast for forty days (Ex 34.28; cf. Deut 9.9-11). And forty days were needed so that the Israelites could receive both the Law, and the design for the Tabernacle, which Moses was to build (Ex 25-26). The same number of days was required before they could be given the priesthood (Num 3.1). Christ fasted for forty days in order to be with His Father, and throughh His Father He triumphed definitively over Satan (Mk 1.13; Lk 4.2).
Thus when Luke tells us that Christ was seen by them for forty days, you know what this means: perfection, completion; a fullness that cannot be surpassed. It designates a perfect period of time during which the One from beyond time revealed Himself perfectly. And he chose to do this, not simply through the medium of time, but through sight, by means of vision, by being seen, because seeing is the most powerful of our senses, and the one which provides us with the clearest and most enduring impressions.