The answer
I recommend reading the book, "The Life of Repentance and Purity," by Pope Shenouda III, which elaborates more on your quest about how to know whether you have a pure heart. In Psalm 51, the Prophet David asked God to create in him a clean heart. Despite some of David's shortcomings, he is known as a man after God's own heart (1 Samuel 13;14; Acts 13:22). Thus, first and always, pray. When Solomon asked God for wisdom, God made him the wisest man in the world and more (1 Kings 3:1-15). Therefore, pray: "Ask, and it will be given to you; seek, and you will find; knock, and it will be opened to you. For everyone who asks receives, and he who seeks finds, and to him who knocks it will be opened" (Matthew 7:7–8).Answered by His Eminence Metropolitan Youssef (opens in a new tab)