"Day" is a symbolically represented certain historical period of time in which the Laws of God's eternal Predestination, all His physical and spiritual creative Laws - for the spiritual formation of Man - are realized.
 "Day" is also the period of time in which Man realizes the necessity of knowing and fulfilling the Revelation of the Light of the Wisdom of God's Will, His spiritual Laws of true Life. 
"The Day" is the time designed and provided for man to carry out the Will of God, His Commandments.
 "The Last Day" is the last period of existence of humanity's sinful history. 
"The Last Day" is the foretaste of the destruction by sins of lawlessness of the vicious system of life of the nations of the world and the establishment of the Kingdom of God's Will, - Righteousness, Peace and Welfare in the nations who obey His Commandments.
"The Last Day" also means the last period of man's life when he still has the opportunity to hear the Word of God addressed to his conscience and mind, to repent of his sins and to change his life.