It's not a metaphor. It's the reality of being a follower of Christ. Many early followers of Jesus understood this reality. But, why quote them? Jesus Himself spoke of this division that would occur.

Look at what Jesus says in the Bible:

"I have come to ignite a fire on the earth, and how I wish it were already kindled! But I have a baptism to undergo, and how distressed I am until it is accomplished!

Do you think that I have come to bring peace to the earth? No, I tell you, but division. From now on, five in one household will be divided, three against two and two against three. They will be divided, father against son and son against father, mother against daughter and daughter against mother, mother-in-law against daughter-in-law and daughter-in-law against mother-in-law.”

— Luke 12:49-53

Love is only one side of the coin. If you love one thing, you have to hate its opposite. You can't love both truth and evil, righteousness and sin.