1 Corinthians 16:8 But I will stay in Ephesus until Pentecost, 9 for a wide door for effective work has opened to me, and there are many adversaries.
Paul was writing to the church in Corinth letting them know he intended to visit them, but he would be delayed a bit. v.8 tells us the reason for the delay. The ministry in Ephesus was too fruitful to walk away from. Then he adds, “and there are many adversaries”.
When the Kingdom of God sees breakthrough there is pushback from the forces that defy God.
I’ve seen this enough times to know it’s true. God uses us to advance the Kingdom (a wide door for effective work) and then problems emerge: division and arguments commence, sickness/illness knocks us down, temptations to sin multiply, obstacles appear from nowhere. My temptation is to back off of praying when things are going well, which is a mistake. It may be the time when we most need prayer is right after seeing the hand of God move among us.
Fuel for the journey 
Disciplined prayer is one of the things I admire about Islam (5 times a day). I do my best to pray 3-time a day, and even then I fear that it sometimes get mechanical instead of passionate.