Welcome Seeking,
Its pretty simple I think. We believe what Christ told us the answer to this question through His conversation with the rich young ruler, when the ruler asked the same question you ask. Jesus said, obey the Commandments and follow me. He specifically told the ruler to sell everything first and follow Christ in His mission. We interpret that to define what it really means to make Christ ones Lord and savior. We must be willing to give up our lives in love for Christ our Lord and follow His will. And His will does include following His moral Code, the 10 commandments, as well to hearing His direction for our lives through the discernment of the Holy Spirit’s urgings. This all presupposes a faith in Christ as God and savior. But faith does NOT just mean belief in Christ as God, but rather faithfulness. The Sacraments, devotions and disciplines are all intended to give us the grace to be obedient to Gods will. We may not necessarily be sinless, but with Gods grace, we will continue to seek holiness. And lastly , we believe the Bible when it says . nothing holy will enter heaven. And “holy” does not just mean an “imputed” holiness through Christs death and resurrection, but our own actual holiness merited through Christs grace flowing through us from the sacraments, our prayers and reading of scripture. While we may not be perfectly holy while on earth, we do believe in the ancient belief in a period after death where we are cleansed of all our sins to make us truly holy for heaven. Purgatory is the place where that cleaning happens to people who will go to heaven but are not quite cleansed of all their unholy ways, so that we may become holy as the Christ commands us to be holy to enter heaven. We object to the notion that those who live a sinful life un repentant manner, even if they profess their faith and discipleship of Christ, will have eternal life.
How do you get that? That wasn’t religion - that was simony. And it’s still a mortal sin even today.