The first is Salat, the prayers five times a day, the continual balance between work and rest, and rest especially in God, in Whom is the only rest of every soul. The life in the world is such that it absorbs every moment of man's time, and the innate yearning for peace that every soul has is never satisfied. Therefore the prayer five times a day is not too much, considering how far the life in the world removes a soul from God. In my mind, if it were a hundred times a day it would be too little.
The second is Zakat, charity. However pious and godly a person may be, however much time of his life he devoted to piety, he cannot deserve the blessing of God unless he is charitable, for charity is the only test of selflessness. All love and friendship is proved by service and sacrifice, and to the extent one is able to do it, one is selfless. And, self being the only barrier that stands between man and God, charity is the only means to break down that barrier, that man may be face to face with God.

Once someone asked the Prophet: "Who is the most blessed, the prayerful, the fasting, the pilgrim, or the charitable?" The Prophet answered: "The charitable; for he can pray, and he can build a mosque for others to pray; he can fast, and he can help those who fast by giving them rest and peace, by providing for the families that depend on them for maintenance; he can make pilgrimage, and he can send many on pilgrimage. Therefore all these four blessings are involved in one, the charitable."
The third duty is Roza, fasting. Man is so dependent on food that even in his infancy, when he is an angel, a king in himself, he hungers after food. This shows that what man needs most in life is food. He will give his diamonds and gold and all his treasure when the time comes that there is lack of bread. Therefore abstaining from food is as abstaining from the dearest thing in life, and sacrificing all comfort, joy, rest, and happiness. As renunciation of lower things is the only means of attainment of higher objects, there can be no better means to attain spiritual life than fasting. Fasting crushes not only the appetite, but the root of all desire that binds the soul, which is the bird of Paradise, to earth's lower regions. Jesus Christ went to the mountain and fasted for forty days against the temptations of the Devil, whom, at the end of fasting, he conquered.
The fourth duty of the faithful is Hajj, pilgrimage. Abraham, the father of the nations, and the fountain from which the streams such as Moses, Christ, and Muhammed came, had made a prayer, as it is said in the Qur'an, when leaving his son Ishmael in the barren desert of Arabia. His heart was broken, and there came out of it a prayer: "O Lord, bless this land, that it may become the attraction of the whole world."

And so it happened in the course of time that the Word of God was born among the descendants of Ishmael, Muhammed, who glorified the name of the Lord of Abraham aloud, which was heard from the depths of the earth to the summit of heaven, and re-echoed from the north to the south pole; which shook the nations and stirred up races, and so pierced through the hearts of men that the desert, which bore no fruit, no treasure of any kind -- no beauty of scenery, no charm of climate -- became a center of attraction for numberless souls, who came from all parts of the world and assembled in that land of bliss, king and pauper standing shoulder to shoulder, both recognizing the equality of men in the Presence of God. The strong and weak, rich and poor, high and low, civilized and uncivilized, all come year by year on pilgrimage to Mecca in this land, clad in one piece of cloth, for all to look alike, and to show to God and humanity the equality of the human brotherhood. This is called Hajj in Islam.