40. Since Christian love is purified, perfected and elevated by Christ's love for the Church (cf. GS 49), the engaged should imitate this model and develop their awareness of self-giving which is always connected with the mutual respect and self-denial that help this love grow. Reciprocal self-giving thus implies more and more the exchange of spiritual gifts and moral support in order to make love and responsibility increase. "The indissolubility of marriage flows in the first place from the very essence of that gift: the gift of one person to another person. This reciprocal giving of self reveals the spousal nature of love" (Gratissimam Sane, 11).