Confirmation and 1st communion must be understood in relation to baptism. I am not a scholar, but I would imagine that confirmation (chrismation) and 1st communion early on were combined with the sacrament of baptism (as is still found in the Eastern Churches). Not only infants, but young adults converting from paganism were brought in as well. Somebody had to attest to their genuine interest in becoming Christian. Hence, the first godparents. When confirmation and 1st communion became distanced from baptism in the West, the idea that one should have a sponsor continued. I know that with confirmation, it is desirable that one’s sponsor be one’s godparent, but this need not be the case. With infant baptism, the godparent promises to see to that the child grow in knowledge of the Faith. With confirmation, the sponsor attests that the individual is ready to receive more fully the gifts of the Holy Spirit. At least, that’s how I understand it without having studied more of it.