Spiritual things only become clear beyond a doubt when the spirit sees them and perceives them. In order to see and feel the manifestations of the spiritual world, long and exhausting spiritual practice is needed, after which, by God’s grace, spiritual vision may be opened in a person; this vision allows him to see what seems unbelievable and impossible to ordinary mortals.
Nevertheless, a person must first believe those who have seen the unbelievable, and strengthen their faith from day to day, striving to see what is inaccessible to the common gaze. Not in vain does the Lord say, Blessed are they that have not seen, and yet have believed (Jn. 20:29). The Lord God rejoices in their faith just as a father on earth rejoices that His children believe his every word.
All the apostles were present at the Ascension of the Lord, gathered on the hill. This was their last gathering. However, this was not the last appearance of Christ. Later He appeared in a vision to the Apostle Paul on the road to Damascus, to the Apostle John on the island of Patmos, and to other apostles, as well as to martyrs, holy hierarchs, and confessors, over the course of the entire history of the Christian Church.
But the day will come—and that day is not far off—when all the righteous mean and women who firmly believed in Him throughout their lives will see Him. And around Him in the heavens will gather all those who were baptized on earth in His name—not only with water, but also with the Spirit and Fire. And they will enter into His joy, which the Heavenly Father has prepared for all His chosen, and will inherit a joy that they have never known before.
St. Nicholai Velimirovich, The Ascension of the Lord