Love without action may be said to be mere sentiment, but true love doesn't need much of a reason.
Giving to charity for example, CAN be born of a belief that people who give will get in return, or out of a simple desire for a tax write-off, and can be done with no love whatsoever. Missionary zeal is different though. If you're gonna keep going, simply believing a theological point is true just isn't going to be enough.
But you're right. You can't love a God you don't believe in.
Yes, I agree, it's important to "keep going," but it's also important to be going in the right direction. Knowing the right direction involves the mind. Unless we actually believe the truths that we are preaching, and are able to give a reason (λόγον) for the hope that is within us (1 Peter 3:15) missionary zeal is not love, but emotional manipulation. I know. I've experienced it.
I grew up among folks who were into winning souls for Jesus, but when I was 12 and wondered about the history of our church, they told me that as Baptists we could trace our origins to John the Baptist. I was incredulous. They loved Jesus all right, but they didn't love the truth, and in the end that made me suspicious of them. For a long time. By interpreting "zeal" exclusively as a matter of the will, they were prepared to evangelize me, but not disciple me. I'd like to think that missionary zeal includes both evangelization and discipleship, but then that means ministering to heads as well as hearts.
My husband went to a well-known midwestern seminary and failed his evangelism class because he refused to lie, and use the ploy of taking a survey as a way to engage folks in the mall with the four spiritual laws. The professor was certainly full of missionary zeal! Unfortunately, his truthfulness didn't match his "love." He loved Jesus so much-- and wanted others to love Him as well-- that he ignored an important theological point: that God is a God of truth, not lies.(Titus 1:2) At the end of the class, the instructor was brimming with joy as each student reported the number of souls saved using this technique. He tallied them on the board and led the class in a prayer of thanksgiving for the success they had been given in evangelizing. I wonder what God was thinking.
So yes. It depends on how one defines "love," and I can't see how genuine Christian love can only be a matter of the will and not also the intellect and the body. (The reverse is true, as well: I can't see how genuine Christian truth can only be a matter of the intellect, as Protestant scholasticism holds, and not also a matter of the will and the body.) I think of Luke 10:27, and how we are enjoined in loving God to use every part of us: heart, soul, strength and mind. ISTM that the only missionary zeal worth offering others is that which reflects the way we are to love Him.
Thanks for this conversation, X! I've really enjoyed talking with you!