1 Corinthians 16:9
For a great door and effectual is opened unto me, and there are many adversaries.
Great Door:  in 1 Corinthians 16:9 is “megas-thura”; signifying exceedingly great, greatest; extremely high or the mightiest of doors.
It also signifies literal as well as figurative gates serving as portals, entrances or openings as well as separating closures.
Great Door:  implies a God-given opportunity to enter in a “great and effectual door” God opens for us to be abundantly profitable and extremely useful in and to His Kingdom.
However, it is also a given that there would be “many adversaries” waiting to challenge our entering in especially with intention of going on through!
Effectual:  is the word “energees” which can be used to mean sufficient to be able to produce the desired effect; here it implies much energy and labor must be utilized to press through the challenging trouble adversaries bring to frustrate ministry in fantastic opportunities.
Yet, remember Paul said with these doors are “many adversaries”!
Adam and Eve were a scriptural example of God expecting us to sacrificially labor to discern and enter into these Great Effectual Doors and press past our many adversaries in the kairos (God’s opportune time) of our times.
Through their example we learned He’s already seen and knows what lurks waiting; creeping in darkness ready to oppose any press on through. Still!
Pressing unto our individual marks for the prize of the High Calling God sets before each of us as joy; is but our reasonable service. Philippians 3:14 
We must press beyond the subtility of many adversaries according to order as God bids us do!
For He blessed and purposed us as believers to also be the “keepers” of His vision just as He powerfully assigned Adam and Woman to tend, guard and keep in the garden.