Forty days after Resurrection Sunday and ten days before Pentecost Sunday is technically the Day of the Ascension, when Christ was assumed to Heaven to sit at the right hand of God (see Acts 1:9-11). In the medieval church (and in the Roman Catholic Church to this day), this was typically considered a feast day. The Catholic Church, citing Augustine, claims that this day was observed from the earliest of times, but there is no documentary record that this was the case before the sixth century BC. Although the day typically fell on a Thursday, the Catholic Church in the past 15 years has moved its observance to the Sunday before Pentecost, partly to increase observance.
Is this a holy day that we should observe? I’m inclined to think not. Certainly, the Day of Ascension begins the period of anticipation in which we look forward to Christ’s return. That said, in the course of redemptive history the ascension of Christ is an intermediate event—a notable event to be sure, but nonetheless, an intermediate one. It is useful to put this into context. Crucifixion Friday (Good Friday) marks the completion of Christ’s sacrificial work done to reconcile His people to the Father. Resurrection Sunday marks Christ’s triumph over death. The next big event redemptively is Pentecost, which marked the outpouring of the Holy Spirit on God’s people in fulfillment of Jeremiah’s prophecy of the New Covenant (31:31-34). Jesus Himself pointed to the coming of the Holy Spirit as the key coming event:
Nevertheless I tell you the truth, it is to your advantage that I go away; for if I do not go away, the Helper will not come to you; but if I depart, I will send Him to you. And when He has come, He will convict the world of sin, and of righteousness, and of judgment… However, when He, the Spirit of truth, has come, He will guide you into all truth; for He will not speak on His own authority, but whatever He hears He will speak; and He will tell you things to come. He will glorify Me for He will take of Mine and will declare it to you.John 16:7-8, 13-14
This priority on the coming of the Holy Spirit is also indicated in both Luke’s gospel (Luke 24:50) and the book of Acts (1:1-8). The significance of the ascension is that Christ’s going was necessary in order for the Spirit to come. Even the angels said that Christ’s going is overshadowed by the fact that He will return again in the same manner in which he left. For this reason, I think it is probably more important to focus on Pentecost as that point in which the New Covenant was formally inaugurated.