Just suddenly think of a question.
It is say that we don’t have desire or can’t sin in Heaven. Why? Doesn’t the souls in Heaven have free will too? Satan and the devils were once angels with free will in Heavens too.
Sincerely seeking for explanation.
Nope, when we are in heaven we will not change our mind; we cannot sin, for we would already had decided that we will sin no more. We made that decision while we were on earth.
Let me try to explain. As Miss Zundrah has so beautifully noted above, both angels and human souls have free will. Now the thing is, as I remember, angels are what St Thomas Aquinas called
intellectual creatures; that is, they already know all the consequences of any action they do, they do not need to learn from experience. Therefore, they have
perfect wills: when they decide on something, it is permanent. That’s why Lucifer and his minions will never ever change their minds about their rebellion: they knew all the consequences of their sin from the very beginning.
Humans, on the other hand, are called
rational beings; that is, we learn from experience. That is why our wills are imperfect; we may will for something, but we do not fully know the consequences of our actions until we experience them. And thus, we may change our minds later, depending on what we learn from experience.
When we die, however, we become “like angels in heaven” (Matthew 22:30); that is, we become intellectual creatures, but our intellects would have been shaped by our stay on earth, illumined by God’s perfect justice. By then, our wills will be perfect. Therefore, like angels, we make that one choice after death: whether we go to Heaven (through Purgatory, if necessary), or to Hell. Along with God’s judgment, we will convict our own selves of damnation or salvation.