Ok I am a little confused. When we die our bodies are supposed to be reunited with our soul after Judgement? If our soul is our “spiritual body” why would we need our flesh body anymore?
The short answer is because Christ has power over death. “If the dead are not raised, then Christ has not been raised. If Christ has not been raised, your faith is futile and you are still in your sins. Then those also who have fallen asleep in Christ have perished” (1 Cor. 15:13–18)."
St Paul tells us, the Christian faith cannot exist without this doctrine, it has been infallibly defined by the Church. It is included in the three infallible professions of faith—the Apostles’ Creed, the Nicene Creed, and the Athanasian Creed—and has been solemnly, infallibly taught by ecumenical councils.
The body and soul were designed by God to be one (personhood). They are meant to be together. The physical body is only separated from the soul due to a physical death which is an unnatural state due to our fallen nature. We were originally designed for everlasting life.
When we die, our soul passes an immediate judgement of where it will spend eternity. If we are in a state of original sin or depart in actual mortal sin the Soul enters Hell immediately. If we die in a state of grace but in need of purification the soul goes to Heaven via Purgatory. If we die in a perfect state the Soul enters Heaven immediately.
“BODY AND SOUL BUT TRULY ONE” CCC
362 The human person, created in the image of God, is a being at once corporeal and spiritual. The biblical account expresses this reality in symbolic language when it affirms that "then the LORD God formed man of dust from the ground, and breathed into his nostrils the breath of life; and man became a living being."229 Man, whole and entire, is therefore willed by God.
363 In Sacred Scripture the term “soul” often refers to human life or the entire human person.230 But “soul” also refers to the innermost aspect of man, that which is of greatest value in him,231 that by which he is most especially in God’s image: “soul” signifies the spiritual principle in man.
364 The human body shares in the dignity of “the image of God”: it is a human body precisely because it is animated by a spiritual soul, and it is the whole human person that is intended to become, in the body of Christ, a temple of the Spirit:232
Man, though made of body and soul, is a unity. Through his very bodily condition he sums up in himself the elements of the material world. Through him they are thus brought to their highest perfection and can raise their voice in praise freely given to the Creator. For this reason man may not despise his bodily life. Rather he is obliged to regard his body as good and to hold it in honor since God has created it and will raise it up on the last day. 233
365 The unity of soul and body is so profound that one has to consider the soul to be the “form” of the body:234 i.e., it is because of its spiritual soul that the body made of matter becomes a living, human body; spirit and matter, in man, are not two natures united, but rather their union forms a single nature.
366 The Church teaches that every spiritual soul is created immediately by God - it is not “produced” by the parents - and also that it is immortal: it does not perish when it separates from the body at death, and it will be reunited with the body at the final Resurrection.235
367 Sometimes the soul is distinguished from the spirit: St. Paul for instance prays that God may sanctify his people “wholly”, with “spirit and soul and body” kept sound and blameless at the Lord’s coming.236 The Church teaches that this distinction does not introduce a duality into the soul.237 “Spirit” signifies that from creation man is ordered to a supernatural end and that his soul can gratuitously be raised beyond all it deserves to communion with God.238