If the human person is body and soul, how can

the soul be truly human when it is separated from the body?
The Catechism explains that it is because of the spiritual soul that the body made of matter becomes a living, human body. The union of body and soul in the human person is not the union of two natures but a union which forms a single nature. The Catechism recalls the traditional expression of this teaching: "The unity of soul and body is so profound that one has to consider the soul to be the 'form' of the body-(365).
Therefore your question is a valid one; we do believe that at death, the soul is separated from the body which then decays, and that the holy souls await the resurrection at the last day. As Pope Benedict XII taught. the souls of those who are saints immediately enjoy the beatific vision before they take up their bodies again and before the general judgment. (Cf Catechism 1023) The difficulty is how to understand that the soul sepa rated from the body is truly human since the human person is body and soul. St Thomas Aquinas considered the question of the separated soul in detail particularly in question 89 of the first part of the Summa Theologica. From his various articles, we can draw out some relevant points.
He explains that the soul separated from the body is still a human soul, it does not become an angel or some other spiritual being, or cease to exist. Nevertheless, the soul apart from the body has a different "mode of being": it exists in a different way and knows things in a different way. It is less perfect when separate from the body since its nature is to exist in the whole human person body and soul.
The Christian doctrine of the resurrection of the body affirms this. Although the saints are perfectly happy immediately after their death, the final perfection of heaven is completed with the resurrection of the body. We are called to enjoy the presence of God for ever as human persons, body and soul.