Even though we have been saved by Christ’s passion and death on the cross, we will not be able to enter heaven until we are fully able and willing not to sin and have learned how to completely align our will with God’s Will and doing only the good (not sin).

It is very likely that our loved ones who have died did not understand this fully before they died and therefore are in need of our help to achieve the holiness necessary to enter heaven. They need to have reached the place of being "fully able and not willing to sin. ... Anyone who has not been completely freed from the tendency to sin is, to some extent, “unclean" and nothing unclean will enter heaven. Through repentance we gain the grace needed to be worthy of heaven. But while we have been forgiven and our soul is spiritually alive, this alone is not sufficient for gaining entrance into heaven. In other words, if a person entered heaven before reaching that level of holiness where even the tendency to sin is gone, they would still be capable of sinning and could therefore lose heaven.

The following is taken from a seminar I took from CDU (Catholic Distance University) entitled "Why Would a Loving God Allow Evil, Pain, and Suffering":

Since we have free will on earth, it seems likely that we will also have free will in heaven. But since the beginning of human history people have used their free will to choose sin and evil. Therefore, how can we have free will in heaven, yet heaven still be without sin and moral evil? In other words, how would heaven be any different from earth?

It seems the answer is that the only people in heaven are those who, by the grace of God, are capable of fully aligning their own free will with God’s will and doing only the good (not sin). For as Jesus taught us to pray in the Lord’s Prayer, “Thy will be done on earth as it is in heaven.” By these words, Jesus showed how important it is for us to follow the will of God on earth. He also implied by these words that God’s will is perfectly followed in heaven.

As St. Anselm wrote, “No one will have any other desire in heaven than what God wills; and the desire of one will be the desire of all; and the desire of all and of each one will also be the desire of God.”[ii] Thus, we are able and willing to do only the will of God when in heaven.

In order to be with God in heaven, we need to be perfect as God is perfect. For as Jesus said, “You must be perfect, just as your Father in heaven is perfect” (Matthew 5:48). We know this is true because God has predestined us for one thing―heaven―where all is perfect and everyone is without sin. For as Scripture states, “nothing unclean shall enter it [heaven], nor anyone who does abominable things or tells lies” (Revelation 21:27).

Anyone who has not been completely freed from the tendency to sin is, to some extent, “unclean.” Through repentance we gain the grace needed to be worthy of heaven. But while we have been forgiven and our soul is spiritually alive, this alone is not sufficient for gaining entrance into heaven.

All Christians agree that we will not sin in heaven. Therefore, we need to be completely cleansed of our sinful tendencies before we can enter heaven. Sin and the final glorification in heaven are utterly incompatible. Thus, it follows that people are unlikely to actually enter heaven until they are fully able and willing to not choose evil.

In other words, without the gift and grace of perfect holiness, which is possible only when we actively cooperate with the power and presence of the Holy Spirit in our lives, we cannot be with God in heaven. Sanctification is the grace-filled process by which we become holy.

This perfection of holiness is not an option. It is not something that may or may not happen before we get into heaven. It is an absolute requirement. As Hebrews 12:14 states, we must strive “for that holiness without which no one will see the Lord.”

Therefore, we need to make a serious effort to deepen our union with God and grow in personal holiness while here on earth. Only when we die to our selfish and sinful desires and achieve perfect union with Christ will we be holy and perfect. Of course, we cannot do this just by ourselves. Rather, we are to humbly act in complete cooperation with the grace and power of God in our lives, especially the sacraments.

Even though we have been saved by Christ’s passion and death on the cross, we will not be able to enter heaven until we are fully able and willing not to sin and have learned how to completely align our will with God’s Will. This helps explain why growth in virtue and holiness should be a primary purpose in our life. Suffering often provides the means by which we are able to grow in holiness.

This makes sense if you really think and pray about this! Lucifer himself was literally in heaven, chose to sin and was cast out.

Fr, Thady Doyle writes in his book "I Want to Go to Heaven the Moment I Die":

"In my own case, without leaving my body, I had the tremendous experience of the love of God in 1972. I experienced myself as being loved by God to the depths of my being; and that sense of being loved by God and of Jesus living in my heart hast remained with me. But it took many years to face the full truth about my life - to recognize the ways in which I was still outside God's will and indeed hurting others; to let go of my own hurts and bitterness; to take the steps to come into healing; and to even basically align my life to God. So too, in Purgatory, one can experience the love of God but one may still have much work to do."

I think this highlights how important it is that those in heaven are fully able and willing not to sin; otherwise, heaven would be no different than earth. How often do we hear this and how should this affect our evangelization efforts?