“God is love,” as Scripture says, and that means the revelation is in the relationship. “God is love” means God is known devotionally, not dogmatically. “God is love” does not clear up old mysteries; it discloses new mystery. “God is love” is not a truth we can master; it is only one to which we can surrender. Faith is being grasped by the power of love.

William Sloane Coffin, Jr. (1924-2006) American minister, social activist

“Emmanuel,” sermon (1979-12-09)
    (Source)

Sermon on Matthew 1:23.

Coffin had used very similar language in an earlier sermon, "Born to Set Thy People Free" (1977-12-04), on John 1:14:

God is known devotionally, not dogmatically. If as Scripture says, "God is love," then the revelation is the relationship. Christianity is not cleaning up old mysteries; it's the disclovsure of a new mystery. It is not a truth that you can master; it's only one to which you can surrender. Faith is being grasped by the power of love.