His point is that since we have received this ministry of the Spirit we do not loose heart. If you have been engaged in any type of ministry you are aware that it can be draining. One can get discouraged by lack of progress or outright resistance.
But look at what Paul contrasts with losing heart, renouncing hidden things, which he describes as walking in craftiness or adulterating the Word of God. That is the pull. To do something unique, something catchy, attractive, sexy to attract people. But here Paul tells us that in the ministry of the Spirit, the issue is not our cleverness, no. The issue is that we have to trust the Spirit to penetrate the darkness that enfolds those whom we wish to reach.
It is not something we can do. It is the Spirit’s work.