There are many things that can keep a church from growing and reaching its potential. The most obvious is for whatever reason God is not able to bless the work and all you are left with is human effort and nothing supernatural can happen.
The list of other real issues includes lack of resources in the areas of staffing, programming and facilities that will prevent you from reaching the next level. Oh by the way, every significant increase of 500 people creates an entirely new list of different challenges that must be addressed in all of these areas.
Sometimes the problem is that a church gets out of balance in any one of these areas to the detriment of all the others. The most obvious is over building your site and incurring too much debt that strangles everything else you are trying to accomplish.
The single most significant issue beyond the blessings of God is the constantly changing role of the pastor and the people. In most small churches the pastor does the ministry and the people run the church. For any church to reach its potential the pastor must do the leading and the people must be equipped to do the ministry.
In my experience far too many times when this ongoing transition breaks down the primary blame is placed on the people and their unwillingness to follow. The hard cold truth is the reason they are not following is there is not a leader in place that has the character and integrity to say clearly come follow me as I follow Christ.