It is Monday, the day after the triumphal entry. This is the divine Son of God.
That could be true of us. There are churches full of activity, all kinds of things going on, bands, orchestras, drama, gimmicks, and crowds. If you were undiscerning you would say, it's a place of life. Is it all leaves? No real conversions, no transformation of life, no people finding and walking with the Lord, no one brought humbly to repentance, given new life and a new nature. Is it all leaves and no fruit? That was condemned by the Lord. So this tree, like the Jewish era, would wither and die. In A.D. 70, Titus the Roman general would lead his troops and destroy Jerusalem and the temple, and there would be no more Jewish temple, and the end of the Jewish church would be completed. The tree was an illustration.
It could also be applied to a single human life. God looks for fruitfulness from us, in the form of response to the message of the gospel. His patience is very great and he bears with those who do not acknowledge him or give thanks to him for many years. But if we are all leaves and no fruit – no praise to God, no appreciation of his gifts, no obedience, no service – then we too are in danger of being cursed.