The Christian believes that the Bible is the Word of God and that it is sufficient to show him the way of salvation. He listens to no other voice except that of God as He speaks through the inspired book. In Catholicism, they replace the Bible by the official pronouncements of their leaders, and though their doctrines cannot always be shown to be biblical, they appeal to their traditions as if they were God's truth. Often, they make the Word of God of no effect by their traditions.
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First, you asked about the fundamental differences between Lutheranism (Evangelical Christianity) and Roman Catholicism. 500 years ago Martin Luther and those who embraced the Biblical Gospel that he had rediscovered, bitterly broke with the Roman Catholic Church, over two main differences. To this day these two differences remain.
Difference #1 is over the answer to the question, "How is one saved and enter heaven?" Martin Luther and Lutherans to this day answer this question with Scripture: "we maintain that a man is saved by faith apart from works" (Romans 3:28; see also Romans 3:19-4:5; Romans 5:1-2; Galatians 2:16-21; Galatians 5:1-5; Ephesians 2:8-9; see also John 3:16; 11:25-26). In other words, Lutherans say that we are justified/saved/enter heaven by faith in Jesus as Savior PLUS NOTHING. Christ died for every sin and all guilt, for every impurity and all that we lack. By His death He offers complete forgiveness and salvation AS A GIFT. We receive that gift by faith, by believing that Jesus died for ME. Our love, our performance, our good works do not and cannot save us in whole or in part. Only Jesus' performance saves us and our faith in Him makes His performance ours. .
Roman Catholics answer: No, we are saved by faith PLUS love and good works. Faith alone in Jesus Christ as Savior does NOT save! Unless faith is completed by love and good works it cannot save us.