Fr G. H. Duggan (March AD2000) rightly insists on the necessity of keeping the commandments if we are to retain the virtue of charity and the life of grace, without which we will be eternally deprived of the vision of God. However, as other correspondents have pointed out, this doctrine must not lead us to deny God's unconditional love. Catholic teachings exist in a certain tension with one another, and error often results from emphasising one aspect of the truth to the point of denying some other aspect, which at first sight seems incompatible with it.
"Conditional love" is generally understood to be the sort of love which is altered if the one loved does not fulfil our wishes or expectations; "unconditional love" is that which remains unchangeable regardless of the actions of the one loved. The Fourth Lateran Council (1215) and the First Vatican Council (1870) both defined God's absolute unchangeability, which seems to rule out any "conditional love" in him.
Our sin can prevent the created gift of sanctifying grace from remaining in our soul, but it is powerless to change God's infinite love, which is nothing other than his uncreated essence.
According to St Thomas, "God loves everything that exists" (ST I, 20, 2) and this "by an act of the will that is one, simple and always the same" (I, 20, 3). In a human sense, Scripture occasionally speaks of God changing, being angry or even hating, but these must be understood metaphorically (St Thomas, SCG I, 91, 96).
John 15:10, which Fr Duggan quotes, does not mention God changing his love for us, but implies that we might cease to abide in his love. In other words, by sin, we can close ourselves off from God's love, refusing to receive the life which God never stops offering. By analogy, the sun can continue to shine, but we can choose not to abide in the sunlight, by shutting ourselves in a dark room. Hell is essentially this free self- exclusion from God made definitive and eternal (Catechism of the Catholic Church, 1033).