Who actually gives the spiritual increase when different ministers plant and water?
God gives the spiritual increase. Paul states that he planted and Apollos watered, and perhaps others had a part, but God gave the increase. The laborers have their roles, yet the result is God's. He alone supplies the increase, making the planting and watering effective.
Les explains that Paul says he planted, Apollos watered, and maybe someone else had a part, but God gave the increase. Les then moves to verse 9, where Paul says all of us together are laborers together with God. To illustrate, Les describes a portable beehive where bees work, the queen is marked, and workers fulfill unique roles—some even clean house for the queen—yet all are part of the hive and work for the same purpose. Paul says that is what believers are: laborers together with God, not just individuals or merely for a local church. The end result is that we are God's husbandry and God's building.
I have planted, Apollos watered; but God gave the increase.