Will we be able to sin in heaven? If not, why not?

No—we will not be able to sin in heaven. As the Bible teaches, we as Christians have been made righteous through Christ’s atonement. As Paul explained, Consequently, just as the result of one trespass was condemnation for all men, so also the result of one act of righteousness was justification that brings life for all men. For just as through the disobedience of the one man the many were made sinners, so also through the obedience of the one man the many will be made righteous—Paul, Romans 5:18-19. In heaven, among so many other wonderful things, we will have the nature, the righteousness of Christ, perfectly and completely abiding in us. To think we could have Christ’s righteousness but yet could sin would be to suggest that Christ could sin. In heaven, God’s delivery of us from sin will be perfected, completed; we will no longer be vulnerable to sin. Even now, here on earth, as Peter said it, His divine power has given us everything we need for life and godliness through our knowledge of him who called us by his own glory and goodness. Through these he has given us his very great and precious promises, so that through them you may participate in the divine nature and escape the corruption in the world caused by evil desires—II Peter 1:3-4. In heaven there will be no evil desires, and we will no longer be at war within ourselves, our new nature and our old, fallen nature. We will be able to fully participate in the sinless perfection of God. This will not be due to innocence, which is the absence of something—in heaven’s case, sin. On the other hand, the righteousness we will experience in heaven will be due to the presence of something—God’s holiness. And God will never withdraw His holiness from us; therefore, we will not be able to sin. And the best part of all? Satan will be nowhere to be found. He will be in the “lake of fire”—hell—for all eternity. He will have no access to us. Never again will we be subject to his lies and temptations. All that will be gone—forever! We will be pure—perfect reflections of the righteousness and nature of the Father and the Son.