1 Corinthians 3:7

So then neither is he that planteth any thing, neither he that watereth; but God that giveth the increase (KJV)

Then: Paul explains the metaphor. The workers in the field have no signficance that they should be picked out to be more important than other workers. Only God, the head of the universe, and the one who occupies the hearts of each individual believer is to be valued, honored and glorified. Through him all things are accomplished. Without him, nothing of eternal consequence will ever be done.

Now: Farming is a necessity for providing life. As a metaphor it has enduring significance and meaning, age after age. Twenty-first century Christians can understand it just as well as first century Christians could. We learn from Paul and Apollos. We are glad for the work they did, but our worship and praise goes to the Lord, for without him our lives are empty.