God has done an amazing job at designing the human body. Case in point is when one has an injury that forces you to not use the injured body part, like a hand, leg, or arm. It is amazing how adaptable the human body is because it doesn't take long to be able to do a lot of the things you are accustomed to with only a minor inconvenience. This extends to those with life long infirmities or disabilities. They get along without them because they have to. And most manage fairly well. This human adaptability, a gift of God for those who would be in the fallen world, has another less useful function. We also tend to live with the infirmities that might kill us.
This extends to the flesh as well, or rather the part that is wholly sinful. It is certainly a challenge with evangelism to show others that they are sinful. This is especially true for those who have been Christian nearly all of their lives, having been baptized as an infant, and know nothing but the warm embrace of the Word. The world is used to their suffering, even embracing it. They don't know they are without God, and without the Spirit’s revelation, they wouldn't care. It hurts to work outside of your normal adaptations. Pleasure and vice are pleasing to the flesh; drowning out the nagging thoughts of failure and hopelessness. Without something to counteract the pull of habit and adaptation, the flesh easily rejects the Word and Faith. The flesh feels it can do it on its own. This is where the Law comes into play, beating the cruel reality against the adaptive mind and flesh, showing its inability to achieve salvation by its own works. The Holy Spirit also bangs away, revealing what God has done and does and will do all for the believers by faith. Some stop fighting the Holy Spirit, stop rejecting the gifts of God. Many on the other hand rage on, fighting the Physician who would cure their disease, preferring abject hopelessness. This warfare is the crux and basis of some evangelism opportunities. No amount of human preparation can prepare one for that type of warfare, but none needs to. This is God's fight- our role is simply to be the messengers of God bringing His life giving Word. God has no infirmities. We shouldn't try and compensate for ours when His Word does it all, and has been since before time.