Bertrande's Growing Love

But gradually Bertrande's affection for her husband became a deep and joyous passion, growing slowly and naturally as her body grew. All about her, life flourished and increased itself, in field, in fold, in the rose-flushed bramble stems of spring before the green leaf unfurled, and in the vine leaves of autumn that lay like fire along the corded branches. She felt this passion within herself like the wine they drank in the early days of spring, light, tart, heady, and having a special frangrance, and her delight illuminated her love like the May sunshine pouring downward into the cupped wine. (26, Lewis)

This passage takes place immediately after the incident between Martin Guerre and his father, when Martin is punched in the face because he'd snuck out of his duties on the farm to go bear hunting. When Bertrande sides with Martin and not the "paternal authority" of the father, whom she holds such a deep respect, her love for Martin starts to grow. Lewis likens this growth to that of Bertrande's body, growing "slowly and naturally," as if this love were a part of the natural process of maturation in girls. Bertrande's environment changes around her as she grows, increasing and multiplying with new life. Bertrande's growth is mirrored by nature around her and thus her love for Martin is likened to the that of spring, and only slightly hinting toward the coming of winter later in her life. This is only a minor suggestion, and, like those of use who rejoice in the beauty of spring without holding back our joy for fear of a later winter, Bertrande's growing love is not mitigated by the suggestion of a later winter, but it grows naturally like the flora of spring. It is also interesting that this love is described without ever giving any ideas as to why she would love Martin. There is no evidence for the cause of this love, only an in depth description of the result. Without including a "because" to accompany these statements of her love, Lewis' description of this love does not answer a deeper question of why Bertrande's love grows as it does. Like the seasons, there is no explicit human motivation for the changes in nature, only the observation that these changes are part of a greater, "natural" process. Thus, Lewis' description leaves quite a bit out of the entire story behind Bertrande's love, and the remaining questions are left to linger in the consciousness of the reader.
Lewis goes on to describe the love like a sip of wine in early spring. This analogy is also twofold: while wine carries the refreshing qualities described in the passage above, it is also "heady," or intoxicating to the drinker. It is not yet clear how this love could be intoxicating to Bertrande, but the fact that Lewis mentions this odd detail suggests that the love is somehow stronger than Bertrande herself, just as enough wine would make anyone woozy with intoxication.
While Lewis' description of Bertrande's growing love for Martin is vague (i.e. it does not describe the cause of her love), it is clear that it is overwhelmingly strong at this point in her life. The contradiction of overwhelming strength and uncertainty leaves the reader slightly uneasy, leaving possibility of lost love open to the future (or the winter, in keeping with the analogy).