Does it matter whether you are the one who plants or the one who waters?
No, it does not ultimately matter whether you plant or water. Both roles are one, and neither is anything by itself, because God alone gives the increase. A believer sows the seed, but God saves. Therefore no one can take credit for salvation; the increase comes from Him.
Les explains that whether we are the planter, the waterer, or whatever other part of the work we may do, that isn't what counts. Neither the one who plants nor the one who waters is anything; God gives the increase. Paul did not take credit for the Corinthians' salvation even though he planted and Apollos watered, because God gave the increase. The planter and waterer are one. Every believer's role is to sow the seed—sometimes just a couple or three words—and then God moves in and finishes that work of salvation. So we cannot take credit for someone's salvation, because we didn't save them; God did.
So then neither is he that planteth any thing, neither he that watereth; but God that giveth the increase.