Paul boldly and famously asserts: “the love of Christ controls us” (2 Cor. 5:14). But what does he mean by “the love of Christ”? If you’re willing to put up with a bit of Greek-grammar jargon, check out this golden nugget in a paragraph from Maximilian Zerwick’s grammar of New Testament Greek. Zerwick writes:
…the objective genitive (Paul’s love for Christ) does not suffice for, apart from the fact that Paul usually renders the objective-genitive sense by εἰς (cf. Col 1,4), the reason which he adds speaks of the love which Christ manifested for us in dying for all men; nor is the subjective genitive (Christ’s love for us) fully satisfactory by itself, because the love in question is a living force working in the spirit of the apostle. In other words, we cannot simply classify this genitive under either heading without neglecting a part of its value. It may also mean the love shown for us by Christ, in His death and resurrection (cf. Rom 4,25!), inasmuch as known (and this through the faith produced in the soul by Christ Himself) and so irresistibly impelling the apostle to return that love.
Let me restate. Zerwick is claiming that the “the love of Christ” does not simply mean Christ’s love for us (what grammarians might call a subjective genitive), nor does “the love of Christ” merely mean our love for Christ (what grammarians call an objective genitive). Zerwick suggests that there is some kind of interplay between Christ’s love for us and our love for Christ. In other words, the Apostle Paul was so overcome with Christ’s love for him (especially displayed in Christ’s death and resurrection) that he himself responded by loving Christ in return. This love-fest of Christ’s love for Paul and Paul’s responsive love for Christ was what controlled Paul, propelling him toward all the sacrifices and hardships he endured for Christ. That’s profound, don’t you think?
What can we take away from this? Let us, like Paul, become so overcome by Christ’s love for us, and so profoundly and responsively loving Christ in return, that we find ourselves controlled by that mutual love to sacrifice and serve and speak on behalf of Christ.
 Maximilian Zerwick, Biblical Greek, trans. from fourth Latin ed. by Joseph Smith (Rome: Scripta Pontificii Instituti Biblici, 1963), 13. So also Daniel B. Wallace, Greek Grammar Beyond the Basics (Grand Rapids, MI: Zondervan, 1996), 119-121, who labels it a plenary genitive.