Luke 13:6-9
6 He also spoke this parable: "A certain man had a fig tree planted in his vineyard, and he came seeking fruit on it and found none.
7 Then he said to the keeper of his vineyard, 'Look, for three years I have come seeking fruit on this fig tree and find none. Cut it down; why does it use up the ground?'
8 But he answered and said to him, 'Sir, let it alone this year also, until I dig around it and fertilize it.
9 And if it bears fruit, well. But if not, after that you can cut it down.'" NKJV
Jesus spent 3 years in His ministry to the nation of Israel (the fig tree) and they did not accept Him as their king. After His crucifixion His apostles had about 40 years (to dig around it). But it never happened so God destroyed the Jewish Temple, and has now offered salvation by grace to all. Up until this time the only way a Gentile could be saved was through a saved Jew. Now everyone is on a level playing field.
There are many ways to interpret this parable, but the commentary you have given does not match the reality.
Please let me explain why.
The Greek word ἔτος could also be matched to the meaning of a season/age and linked to Exodus.20:4-6 which tells us the following prophecy: -
Exodus.20:4-6: - 4 "You shall not make for yourself a carved image — any likeness of anything that is in heaven above, or that is in the earth beneath, or that is in the water under the earth; 5 you shall not bow down to them nor serve them. For I, the Lord your God, am a jealous God, visiting the iniquity of the fathers upon the children to the third and fourth generations/age of those who hate Me, 6 but showing mercy to thousands, to those who love Me and keep My commandments.
This prophecy of the idolatrous worship practices of the Israelites over four ages of their existence matches the same time span of the Parable of the Barren Fig Tree. Israel had been constantly been told that they would be punished for their idolatry which means that that at the end of the first, second and third age, there would be no fruit on the fig tree because of their continual idolatry.
The Parable of the Barren Fig Tree provides a warning to Israel that God was not happy with Israelites and wanted to have the fig tree removed from Hi vineyard, but the keeper of the vineyard, Jesus, pleaded for one more season/age before deciding the Israelite's fate. If at the end of the fourth season/age, there was no hint of any fruit, then yes, the Fig tree should be destroyed.
The parable was a warning for all of nation of Israel's descendants. If they did not repent, then God would destroy them. Since we have not yet reached the end of this present age of the fourth age, it is still too earlier to condemn Israel to the dung heap.
Jesus in Luke.14:30-31 suggests that Israel will at the end of this age seek out His terms for peace and in Luke 19:14 Jesus indicates that at the end of this present season/age that Israel will declare that they no longer want to serve Satan and in doing so they have accepted the terms on offer from Christ of His peace.
What is the event that unfolds at the end of this age? The prophesied 2,300 years of the Gentile heathens trampling the Sanctuary of God comes to its completion and the Heathen Kings of the World will be Judged at Armageddon and as Paul tells us that during or shortly after this event all of Israel will be saved.
Now you have referred to God having the Temple being destroyed in 70 AD and your rational for your statement is that Israel did not repent of their idolatrous behaviour at this time, when in fact God had already allowed the visitation of their inequities upon the Nation of Israel during the third and the fourth age which started with the birth of Christ.
Why was the temple actually destroyed? It was destroyed because in Daniel.9:24 we were told that a new redemption for sin would be put in place after the 490 years of Grace granted to Israel to repent of their sins.
Daniel.9:24: - 24 "Seventy weeks are determined
For your people and for your holy city,
To finish the transgression,
To make an end of sins,
{and after this time of grace}
To make reconciliation for iniquity,
To bring in everlasting righteousness,
To seal up vision and prophecy,
And to anoint the Most Holy.
If a new means to establish reconciliation for iniquity was made through the crucifixion, then no more animal sacrifices in the Temple was required from that time onwards. If no more sin sacrifice are required then the temple needed to be levelled and desecrated such that no further sin sacrifices could be made on the Temple Mound by Israel.
Now after the end of this present Age, God will gather the Israelites to Himself through establishing a relationship with the Israelites where they are found at that time scattered throughout the whole earth. God is not yet finished with the Israelites unless the Israelites do not repent of their idolatrous iniquities.
Shalom
