There are an overwhelming number of scriptures that indicate that faith in Jesus Christ is all we need to obtain salvation. For example, in Acts 16:30-31, The jailor asked Paul and Silas "What must I do to be saved?" and their response was, "Believe in the Lord Jesus Christ and you will be saved." This is very straightforward. All you need is faith.
Additionally, a person must continue to grow in his faith. As a believer matures, his faith is clearly demonstrated by his works, “Faith without works is dead.” (James 2:17) The entire book of James seems to indicate this. Verse 24 of the same chapter reads "You see that a person is justified by works and not by faith alone."
In the Old Testament, there was a strong emphasis on works over faith. The Israelites were given a law or set of rules which they were to obey (works). But no Israelite was able to keep the Law and thereby become justified by his works. Galatians 3:10, 11 (NLT), “But those who depend on the Law to make them right with God are under His curse, for the Scriptures say, ‘Cursed is everyone who does not observe and obey all the commands that are written in God’s Book of the Law.’ So it is clear that no one can be made right with God by trying to keep the law. For the Scriptures say, ‘It is through faith that a righteous person has life.’”
Those faithful people in Old Testament times were not the ones simply trying to follow God's rules. Hebrews 11 clearly gives multiple examples of righteous Old Testament figures who were counted as such "by faith." In other words, because these had true faith, they were able to accomplish great works and they were thus seen as righteous.
This is the key. Faith and works are very much intertwined. One can say that they believe, but a real faith is far deeper than that. James 2:18 unlocks that detail for the rest of the book, "Someone may say, 'You have faith and I have works.' Show me your faith without any works and I will show you my faith by my works."
What the author is expressing is that a true faith will always be accompanied by works.
One can perform many great works without faith, but if you have true faith and are not deceiving yourself, then your behaviors will follow and your actions will reflect your burning faith.
The righteous shall live by faith (Rom 1:17, Hab 2:4, Gal 3:11). Those who have an honest faith in Jesus will have a lifestyle that matches. They will LIVE BY faith. Not that they will simply have faith, but that they will live by it. Any who really comprehend the power and grace of God and his beautiful redeeming salvation cannot help the zeal that produces "good works." (See Jeremiah 20:9, when the prophet could not stop speaking God's word because of the burning fire within him).