So we see that they could not enter in because of unbelief. Hebrews 3:19
It was not the will of God that Israel should wander forty years in the wilderness; He desired to lead them directly to the land of Canaan and establish them there, a holy, happy people. But "they could not enter in because of unbelief" (Hebrews 3:19). Because of their backsliding and apostasy they perished in the desert, and others were raised up to enter the Promised Land. In like manner, it was not the will of God that the coming of Christ should be so long delayed and His people should remain so many years in this world of sin and sorrow. But unbelief separated them from God. As they refused to do the work which He had appointed them, others were raised to proclaim the message. In mercy to the world, Jesus delays His coming, that sinners may have an opportunity to hear the warning and find in Him a shelter before the wrath of God shall be poured out. (The Great Controversy, 458)
Reflection: God wants so much to come again. The delay is not His fault, but ours. We can hasten that day, and are actually responsible to do this. Let's go forward today instead of backsliding.