A plant without roots (or deep enough roots) will not grow. It will not flourish. Plain and simple.
This garden scenario portrays a spiritual truth for you and me as God grows in us a heart of faith: We must nurture a root system! Roots make all the difference in the health of a plant, and their presence or absence ultimately becomes known to all. THe plant either flourishes or fails, thrives or dies, blossoms or withers. The health of anything - whether a garden plant or a heart devoted to God - reflects what is going on (or not going on!) underground. (Elizabeth George - A Woman After God's Own Heart)
Our lack of producing spiritual fruit could be a root issue. We may get all the other things we need to grow - water, sunlight, care - or in this case, Church body fellowship, Prayer, being involved heavily with ministry and Bible reading - and STILL miss the point! Being rooted and in genuine fellowship - no worship! - of God! Those things - the things we do while people are watching - are fine and dandy, but what happens when we get alone with God. What does that time with Him look like? We can do all the "Christian things" on the outside, but it is all in vain unless we are rooted in the truth of the Gospel and it is there where our foundation is laid. Just like our quiet time - our personal time of growth - with God, roots are hidden from the public eye! But the evidence and quality of our roots - our quiet time with God - is found in the fruit that it produces...