Ascension Day is not a festival in all countries. This is due to the fact that people do not understand what it represents. Believers however are supposed to understand it. But even amongst them not all do. What is written about it in the Bible?
Ascension Day is the day on which the Lord Jesus was taken up to heaven. According to the Bible He then returned to His Home (Jh 6:38). Although He lived as Human on earth for a while, He already lived for centuries in heaven. Ascension Day thus is the restoration of the normal order: A heaven Dweller returned to His Own place.
Ascension Day however represents something bigger still. That He will continue His work there. Also, it was joined with the promise that He in the same way – voyage between those two worlds – will return to earth (Acts 1:11). In short, Ascension Day says something about the status of the Lord Jesus and about the continuation of His work. What’s the background of that?
Arrival of the Son
Although humans were not continually aware of what existed in heaven and what happened there, the incarnation of the Son of God was a new revelation for them . Whilst the dream of the patriarch Jacob had revealed that a constant and intensive exchange between heaven and earth exists (Gn 28:12) , nobody realized that God really had a Son in heaven. On earth He announced His existence in heaven since the origin of Creation (Mt 13:35), but that He was sent to earth as part of His Plan (Jh 3:17).
When He came, Israel was on a ‘dead track’. The Jews had a burning desire to become independent again after a period of more than 500 years of occupation. But independence is only achieved by either bringing the enemies under control or by making an alliance with them. Many Jews in those days did not seek independence from the Hand of God, but through their own effort.
Gaining independence in the case of Israel – it being the property of God – is of course to be given by God. To achieve that He gave the previously used  messianic ministry. However, it was not the right time for Israel to have independence, but it was time for their very long-awaited return to God . Although the coming of the Son of God would ultimately lead to their independence, He thus came for the first time as Bible Teacher. Not as their Messiah.
Because He fulfilled the Pésach sacrifice by His death through torture, He did initiate the ministry of God’s Messiah. A ministry for which His Father trained Him. However, the meaning of that sacrifice seemed incomprehensible and too spiritual for Israel. So, they purposely rejected both the way of God towards their return to Him and His way to independence. By doing that they made their guilt complete .
Continuation of hidden good
Still, the Son was able to convince a core of Israel of the message of God, so they took upon them the New Covenant of God which His Son mediated. After that He needed to return to heaven. Just as Moses ‘disappeared’ right before Israel entered the promised Land, so the Lord Jesus ‘disappeared’ right before the people of God fulfilled their assignment. By the death of Moses, the supreme position of the High priestly office of Aaron’s house became the intended spiritual focal point.
The Lord Jesus in His earthly ministry followed up Moses as mediator of the Covenant of God (Dt 18:17-19), but in heaven he followed up Aaron’s office as high priest. This shows the divineness  of the Lord Jesus: He is both successor of Moses and of Aaron, but not only by following them up, but also as their Fulfiller. He is greater and different then Moses and Aaron. Moses helped Israel to become delivered from the power of the pharaoh, but the Lord Jesus did that with the power of satan. Aaron’s service could only give partial and temporary reconciliation, but the Lord Jesus gave continuous and deeper reconciliation.
But what the Lord Jesus accomplished was between God and the believer, since Israel as a nation had rejected Him. His redemption and reconciliation can, for the time being, only be accepted by individual believers . But it is not represented in an institution. Not visible for the world. In the world Israel was banished by God and the Temple was destroyed and this has caused confusion. This explains why Christianity emerged and the church was instituted .
Necessity of ascension
In the Bible the concept of necessity of things is brought forward. It was necessary that the flood came in the days of Noah, that the builders of the tower of Babel were confused and dispersed, that Abram went to Canaan, that Ismael was separated from Isaac and Esau from Jacob, that Israel was delivered from Egypt, that Israel was formed as a nation within the people of God and also that Moses disappeared . Likewise, it was necessary that the presence of the Lord Jesus was ended on the earth. He had to return to heaven. God had commanded it.
Naturally, this latter necessity was not always understood. Not by the people who had walked with Him, but even more so not by generations of believers who were confronted with the fact. Often they even not accepted it coming from the Hand of God. Take for example Job, who resisted the acts of God. But even his suffering was necessary in the whole of the plan of God.
What was the necessity of the ascension of the Lord Jesus? First of all, it has to be clear that He really died and thus, according to human reality, He was already phased out. However, He was raised from the realm of the dead in a glorified Body, which showed that God had opened the way for the believers to live a glorified life in the new Creation . In the current Creation Someone with a glorified body has no place.
Then there is the given that His mission as Bible Teacher and Mediator of the Covenant on earth had ended. He had to make room for the apostles, prophets, shepherds and teachers who needed to follow up on His inheritance.
Above all there is the given that He was ready to go on to the next phase of the fulfillment of His training to become the Messiah of God. After He gave Himself as Pésach offering to God, the ministry of kohen gadol (Israelite high priest) in the Temple of God in heaven awaited Him. Taking up this position was becoming urgent since the Temple on earth was about to be destroyed . The believers  had to be able to rely on His daily service of forgiveness and reconciliation. But He also made room for the Holy Spirit (Jh 16:7), Whom God would pour out on His people, as was previously promised (Joel 2:28) .
The fortieth and tenth day
Why does Ascension Day fall on the fortieth day after Pésach (Passover)? Between Pésach and Pentecost are 49 days. These days are rightly counted in Judaism (the so-called Omer counting). Pentecost is the fiftieth day after Pésach, after the Greek meaning of the Greek word Pentacote. So, the whole period thus is marked by the commemoration of the exodus from Egypt and the going up to the promised Land.
Christians often think that this is only a matter for the nation of Israel and that it doesn’t concern them. Since, as described above, Israel was dispersed by God. Although Christians currently do represent the people of God on earth, that does in no way make Israel irrelevant to them.
The fortieth day is not only relevant for the necessary ascension of the Lord Jesus. It also is connected with the fulfillment of Pentecost. Pentecost is the conclusion of the Pésach period, but God also chose to fulfill His promise to pour out His Spirit on that day. With these acts He emphasized again the preceding fulfillment of Pésach from the Old Testament by the salvation work of the Lord Jesus. Because the Father did that, He also fulfilled Pentecost from the Old Testament. It shows the cooperation between the Father and the Son or, to describe it even better, the confirmation of the Son by the Father. God showed with it the original connection between Pésach and Pentecost which also exists in Judaism. However, that connection is not so clear in Christianity.
The fortieth day is relevant, since it also is the tenth day before Pentecost. The Lord Jesus used the almost 40 days He had left on earth to show Himself to the believers. With that He wanted to take away any doubt or confusion amongst the confused under the believers, like the apostle Thomas.
The number 40 has several meanings, but the number 10 represents human fullness and the number 4 represents the earth. The number 40 thus represents the completion of His earthly mission and the short while of Him being a Human.
In Judaism the tenth day also has a special meaning. It refers to the Day of Atonement (Jom Kippoer): the tenth day of the seventh month . The Ascension Day was ten days before Pentecost. This shows that the salvation work of the Lord Jesus is connected with the final judgment of God since that is also the theme of the Day of Atonement. He averted that final judgment  for them that entered into the New Covenant.
Beginning of the important intermediate phase
Ascension Day represents the beginning of the intermediate phase. His coming as Bible Teacher, Mediator of the Covenant and His Pésach Sacrifice mark the beginning of the Messianic era: the coming  of the Kingdom of God to earth. His resurrection was something extraordinary, something of the new creation in the old creation. The believers have seen Him in that resurrected state for almost 40 days. As preview to what surely is going to happen through God. But this of course could not continue.
He returned to heaven, where also the Father dwells, to perform the Temple service to God. A packed and busy ministry, even more so since satan is distressed through all these events. Thus, the salvation plan of God unrolls until the moment He will give His Son the sign to take upon Himself the ministry of Messiah of God and descend from heaven  in order to pacify His enemies.
 A confrontation with the activities in heaven.
 This is an indication that heaven is strongly concerned with the physical world.
 Moses was the first to have that position.
 Actually since the return out of their first banishment around 537 BCE.
 Shortly thereafter happened for what they were warned; they were dispersed amongst the nations.
 Superhuman and of heavenly origin.
 However, within the collective bond of the people of God and the New Covenant.
 But Christians began clinging to political power with all its negative consequences.
 God killed him.
 However, He did not abolish death, since that abolishment is yet to happen (Rev 20:14).
 What actually happened less than 40 years later (70 CE).
 Especially the believers that took upon themselves the New Covenant had accordingly rightful access to it.
 The Holy Spirit facilitates the transfer of the forgiveness and the blessing by the service of the Lord Jesus in the Temple in heaven.
 On the Biblical calendar.
 Still, Jom Kippoer is not yet fulfilled. This is set to happen in the Messianic Kingdom. Since that is about the future redemption of the guilt of Israel.
 That is marked by being already present, but not yet fully.
 This also will be a unique happening. Incomparable with His incarnation, since He shall not be again born from a sinful human (i.e., born the natural way in a mortal human body). There can be no doubt that He will certainly return in His glorified Body.