"For whoever keeps the whole law and yet stumbles at just one point is guilty of breaking all of it. For he who said. 'Do not commit adultery,' also said, 'Do not murder.' If you do not commit adultery but do commit murder, you have become a lawbreaker." NIV translation
James is pointing out the simple fact that sin is sin. It seems today that we act as if some sins are worse than others but, in reality, God sees them all as disobedience. James points this out to make us see that not honoring the poor is just as bad as murder or adultery in God's eyes.
"Speak and act as those who are going to be judged by the law that gives freedom, because judgment without mercy will be shown to anyone who has not been merciful. Mercy triumphs over judgment!" NIV translation
Once again, James is not talking about becoming saved by works. He tells us to "speak and act" as if we are under the law not to show mercy to become saved. He is simply saying that, if we are saved by Jesus Christ, we will demonstrate mercy to the poor and others because of the love that is in us through Jesus. We, as Christians, will be judged on our words and actions but it is not a judgment of salvation it is a judgment of rewards.
"What good is it, my brothers, if a man claims to have faith but has no deeds? Can such faith save him? Suppose a brother or sister is without clothes and daily food. If one of you says to him, 'Go, I wish you well; keep warm and well fed,' but does nothing about his physical needs, what good is it? In the same way, faith by itself, if it is not accompanied by action, is dead." NIV translation
Now, James tries to reason with the readers and gives us a practical example. He asks us to look at the case of someone who doesn't have proper clothes or food and ask ourselves what good it is to give that man words. He will still be hungry and cold. In the same way, if we say we have faith and yet that faith does not bring about change in our lives, we have to examine our faith and our walk with the Lord.
"But someone will say, 'You have faith; I have deeds.' Show me your faith without deeds, and I will show you my faith by what I do." NIV translation
Once again, James shows us that deeds do not stand alone and cannot save us. But, he also shows us that, if we are saved, our faith in Jesus Christ will cause us to demonstrate it through our actions. We must understand that God does not need our works as He created everything by simply speaking. But, He gives us the opportunity to serve Him so that we may bring Him glory and so that others may believe in Jesus Christ.