In the Parable of the Sower, Jesus had described His message as the seed of the Kingdom of God. That seed planted by His followers is an urgent plea for all to hear to repent immediately of offensive behaviour and to seek reconcilation with God through Him.
Thus far, He had explained that reacting either with hostile prejudice or short-lived loyalty to this priority for our lives is part of the outworking of God's judgement. Jesus resorted to speaking in parables because it requires perseverance to make sense of them.
In contrast, for those who were fickle-hearted or dismissive, the significance of Jesus' illustrations would remain obscure. Jesus echoed Isaiah's promise of judgement on persistently faithless people: 'They may be ever seeing but never perceiving, and ever hearing but never understanding; otherwise they might turn and be forgiven!' (Isaiah 6:9,10)
So, in this parable, the thorns represent the cares, pleasures and distractions of earthly life. Nevertheless, let's be clear that thorns do not destroy healthy crops directly, they simply deprive the good seed of the sustenance required for growth.
This really boils down to deciding where we expend our emotional energy. Being overly focused on the concerns, comforts and diversions of this present life will slowly but surely erode the prioritisation of God's principles for our lives.
Of course, in this regard, it's fairly easy to recite the word (e.g. 'Do not love the world or anything in the world. If anyone loves the world, love for the Father is not in them.' 1 John 2:15 and 'And be not conformed to this world: but be transformed by the renewing of your mind' Rom. 12:2)
In churches, just like any other organisation, members can end up jockeying for prestige more than responsibility, authority and prominence more than exemplary deference and creature comforts more than the cross. Keeping the weeds at bay requires cultivation, which often involves taking a 'hard spade' to an unruly heart.
Being doers of the word requires perseverance that is granted to those who truly despair of their weakness before God, as St. Peter did.
As Christians, we must rely upon Jesus as He works through scripture, the example of fellow believers and life experiences to expose and uproot the thorns of misguided priorities in our lives.
We must also rely upon the assurance of invincible intercession which He gave to St. Peter: 'But I have prayed for you...that your faith may not fail. And when you have returned, strengthen your brothers.' (Luke 22:32)
Yielding our lives to the power of Christ is really about giving in to the leading of the Holy Spirit. Through Him, the thorns really don't stand a chance!