No, Paul was not speaking of cremation in 1 Cor. 13:3. That is a misuse of Scripture. If that were what Paul were teaching, we should see both Testaments presenting multiple examples of where believers cremated others and were lauded for doing so.
Your final paragraph is totally irrelevant. No one in this thread has even remotely suggested that they are saved by their own good works or that we earn righteousness before God by what we do.
Indeed so, St. Paul was providing an extreme scenario of giving away everything to the poor and neglecting even his own funeral, which would have resulted in the Pagan Roman Empire cremating him likely with other bodies, in order to say that if he engaged in such supererogatory almsgiving without love being the motivating factor, it would be worthless.
However such a case of supererogation which is not required of us by God would still be wrong in the cremation process itself, because to cremate a human body according to Jewish and Christian doctrine would not itself be loving. Indeed I would note that part of the extreme example St. Paul provides is that it lacks any love for the divine image; while in Christianity we are not to love ourselves*, we are to love God, and we are to respect the body, even our own, as a temple of the Holy Spirit, and treat it accordingly. On this basis I reject tattoos as generally sinful and am prepared to tolerate them only among certain Middle Eastern and Herzegovinian Christians who use them as a means of reducing the risk of their child being forcibly converted to Islam without at least being aware of their Christian origins, since the cross on the right wrist serves as an ever-present visible reminder of baptism. Among the Maori people and other Pacific Islanders likewise I am prepared to tolerate it, but without the deep religious respect that I have for the practice among Christians, and that is mainly because of certain injustices committed by Europeans against Pacific Islanders. That said, at a future time it would be ideal to discourage them from the practice. Right now tattooing has become something of an epidemic, with even police departments permitting extensive visible tattoos including “sleeves.”
Thus, we cannot cremate ourselves without doing violence to the Divine Image, but most of us are not aware of this, and there are some people who find the natural process of decomposition to be so disturbing they would rather be cremated so as to avoid being in that state. However, this is a mistake on their part, an error, and one that results I think from a lack of veneration of sacred relics of the departed saints; our veneration of these relics which include skulls, bones and also miraculously incorrupt parts of bodies or entire bodies results in Orthodox and Catholic Christians being able to recognize the image of the divine even in those who have reposed in a state of grace, and whose remains are thus blessed and have not completely decomposed, and in many cases exhibit other supernatural properties, for example, myrhh-streaming (which is widespread, the most famous case being the myrhh-gushing skeletal remains of St. Nicholas of Myra, which were stolen by the Venetians if I recall, and are now in an Italian town called Bari, but which continue to stream myrrh which the Catholics make available to Orthodox pilgrims, as they did before they were expropriated).
I myself while on a pilgrimage to the Monastery of St. Anthony in Florence, Arizona, had the opportunity to venerate the skull of St. Joseph the Hesychast, in 2015, which was an extraordinary experience, along with my encounter with Elder Ephraim, memory eternal, who was a sincerely loving Christian who sought to keep the fire alive in the Greek Orthodox Archdiocese of North America, which is controversial among the Eastern Orthodox due to its various problems with ethnocentricity and modernism, which have unfortunately lead to many people joining the ranks of the schismatic Old Calendarist churches, some of which in my opinion have cult-like features. I have had consistently unpleasant experiences with certain Old Calendarists, perhaps because I disagree with their fundamental assertion that all ecumenical dialogue constitutes a “pan-heresy.”
*indeed some Church Fathers speak negatively of self-esteem (although what they mean by it is not how it is used today, to represent the basic confidence and security that many children lack, but unfortunately in our society we have used the phrase “low self-esteem” to refer to this problem, which can be the result of poor parenting, or bullying, or many other things, but which is an acute suffering on the part of children).