This episode is in two parts. We read the first bit today; and its sequel is in Mark 11:20-21, sandwiching (and amplifying) the account of the cleansing of the temple.  Like many things Jesus did and said, this was shocking to His trainee apostles.  But like every shock, it was memorable; which is what Jesus intended as their apostleship needed to be framed not just by glory but also the judgement to come.  

Speaking to trees is not a normal human responsibility, but their Creator has authority to do so - as He did with the wind and waves (Mark 4:39-41).  This episode is really a parable, showing Jesus' power and authority to judge.  Just before Passover, in March or April, fig trees should have green edible buds: these were not the figs that would be harvested later in the year.  But they made a tasty snack - and were evidence that the tree would bear its full fruit later in the year.  Jesus stopped to inspect the tree; it looked healthy, the leaves were rich and green ... but there were no tasty green buds at all.  That tree was not 'fit for purpose'.

The disciples understood that Jesus had cursed the tree (Mark 11:20-21).  The question in their minds was probably, 'Why'?   The answer was already in Jeremiah 8:13, "I will take away their harvest, declares the Lord.  There will be no grapes on the vine.  There will be no figs on the tree, and their leaves will wither.  What I have given them will be taken from them."  The metaphor is about faithless Israel, like Jesus' comment in Mark 12:9.  So, it also pointed forward to the opening of the gospel to the Gentiles.

When Jesus cursed the tree, He demonstrated how His judgement would fall on Israel (Matthew 3:10).  Like the tree, His people looked fine, but were unproductive for God's kingdom. There comes a point when there are no more chances. When Jesus cursed the tree, His Word alone was enough to sap the life out of it.  And that is what will happen to all who refuse to receive God's Christ (Matthew 24:36-44).  

As the disciples were intended to overhear, so are we.  We need to understand that Jesus will judge powerfully, and when He speaks, it is always done (Isaiah 55:11). The outcome for the fig tree was to prove disastrous.  So it will be, for all those who show no sign of spiritual fruit - no evidence of God's indwelling Spirit.  That is why we are called to be Gospel people, men and women with the message of how to be saved from the wrath to come.  Such Gospel proclamation is evidence that we, ourselves, have been convicted of sin and righteousness and judgement.  As Paul says, "Since, then, we know what it is to fear the Lord, we try to persuade others ..."  (2 Corinthians 5:11).  That responsibility shaped the apostles and should continue to shape the church; it is a  responsibility we cannot ignore.