I think the genius of John Paul II with respect to marriage is that he realized that the end of marriage, its final cause, is theosis, the participation in the life of the Trinity. From that vantage point the three ends of marriage as taught by the Church serve the processes of kenosis and henosis as well as metamorphosis. Procreation, the first end, instantiates the creativity of Trinitarian love. This must be the first end of marriage since creativity through procreation grounds the marriage in the full exchange of love present in theosis. The temptation to avoid procreation is the temptation to mistake pleasure in the conjugal relation as the ultimate good and to avoid the necessary suffering of kenosis that is part of the gift of self, and thus miss the joy of Godly love.
In a similar way, the second end must itself be secondary since the temptation to stay focused on the vivid pleasure of the conjugal union will block the necessary grieving of kenosis. The attentiveness that John Paul II focuses on the translation of the Latin describing the second (“mutuum adiutorium”) is characteristic of his understanding on this temptation. This is the temptation to mistranslate the second end as “mutual love” rather than “mutual help”, to focus on the pleasures of the relationship rather than its final cause. The mutual help of marriage is to aid each other to risk the seemingly endless steps of kenosis and their resultant suffering, to “love the Hell out of each other”, to encourage each other to empty themselves of their selves to make an opening for the love of God. This emptying of the spouses allows the filling of new life in the couple and the practicing of theosis, of loving each other as the Trinity love. Thus, the mutuum adiutorium serves the rigors of procreation and its fruits.
Perhaps Karol Wojtyla does not focus much on the third end of marriage (remedium concupiscentiae) in this section because the first chapter is so focused on the explication of the personalistic norm. Certainly he does deal with the subject later chapters and in the Theology of the Body. I sense that he wants to stay focused on the “positive” part of sexual ethics, especially initially on the how love is antithetical to utilitarianism, to avoid perhaps getting distracted by the (contemporarily) recent historical negativity of discussions of concupiscence and its remedy. Certainly a focus on concupiscence would limit the discussion to the subjectivity of sensuality and affection and miss the mystery of Trinitarian love.