it must be believed and it must be lived

So also is love known by its own fruit and the love of which Christianity speaks is known by its own fruit - revealing that it has within itself the truth of the eternal. All other love, whether humanly speaking it withers early and is altered or lovingly preserves itself for a round of time - such love is still transient; it merely blossoms. This is precisely its weakness and tragedy, whether it blossoms for an hour or for seventy years - it merely blossoms; but Christian love is eternal. Therefore no one, if he understands himself, would think of saying of Christian love that it blossoms; no poet, if he understands himself, would think of celebrating it in song. For what the poet shall celebrate must have in it the anguish which is the riddle of his own life: it must blossom and, alas, must perish. But Christian love abides and for that very reason is Christian love. For what perishes blossoms and what blossoms perishes, but that which has being cannot be sung about - it must be believed and it must be lived.

Soren Kierkegaard, Works of Love (26)

How can we better compare this love in words and speech than with the leaves of the tree; for words and expressions and the inventions of speech can also be a mark of love, but they are uncertain. The same words in one person's mouth can be very significant and reliable, in another's mouth as the vague whisper of leaves; the same words in one man's mouth can be like "blessed nourishing grain," in another's like the unfruitful beauty of the leaves.

Ibid (29)