Only Matthew uses the phrase “kingdom of heaven.” Mark, Luke and John prefer “kingdom of God.”
The reason is that the other writers want to emphasize the rule of God at all times in the lives of his people. And so, if you would come under God’s rule here on earth, according to Mark, Luke, and John, you must behave in a certain way. On the other hand, Matthew’s view is further reaching. If you would be a part of the kingdom of heaven, that is, the age to come, you must learn to let God rule in your life now.
If the two views seem the same, keep this in mind: Matthew’s readers are suffering for their faith. Matthew refers to persecution more than the other gospel writers put together. He cannot tell them their trials will soon be over. He cannot say that God will make them painless, or even less painful. What he does do is point them to the eternal assurance that is theirs because God rules their lives. This is the significance of the “kingdom of heaven,” and it is so important, that it becomes, in Matthew, the substance of John the baptist’s preaching, and of Christ’s.
The old hymn reads: “There’s a great day coming, a great day coming.” Whatever we face today, for good or ill, it will be nothing compared to the greatness of the day to come. Whatever we face today, we must live this day to enjoy that particular day to come.