There are factors working against the individual believer which in my opinion, also seek to work against the mission of the Church, as it is a greater extension of the believer. Saint John recognized these as "the world, the flesh, and the devil". I'd pose that "the flesh" (a.k.a "Us") is the single greatest impediment.
The "world" (not to be confused with creation) has stood in opposition to the church since her birth. At its best this world is indifferent to mildly antagonistic towards the church and at its worst, proactively hostile. But the world is a known variable that we've known about since Christ spoke to us on the issue (...If the World hates you...) The very fact that the church exists in places like North Korea, Saudi Arabia and Myanmar stands in testimony to its ability to impede its mission.
What can be said about the adversary that's not already been said? Luther said it well when he penned:
For still our ancient foe
doth seek to work us woe;
his craft and power are great,
and armed with cruel hate,
on earth is not his equal.
This accuser could, left unchecked, smash the the church into dust and scatter it on the four winds. This same accuser is also, under the submission of the Almighty and can only execute what is permitted. The very Lord who promised that the "Gates of Hell" would not prevail against the church, will not permit Hell's dark slumlord to do so either.
This leaves us with the big Mea Culpa; We have met the enemy and he is us, as both Walt Kelly and the Underground Pewster have opined. I'll explain in my next installment.