"Not every one that saith to me, Lord, Lord, shall enter into the kingdom of heaven: but he that doth the will of my Father who is in heaven, he shall enter into the kingdom of heaven." - Matthew 7:21
"For in Christ Jesus neither circumcision nor uncircumcision has any value. The only thing that counts is faith expressing itself through love." - Galatians 5:6
"And this is love: that we walk in obedience to his commands. As you have heard from the beginning, his command is that you walk in love." - 2 John 1:6
"We know that we have come to know him if we obey his commands. The man who says, "I know him," but does not do what he commands is a liar, and the truth is not in him. But if anyone obeys his word, God's love is truly made complete in him. This is how we know we are in him: Whoever claims to live in him must walk as Jesus did." - 1 John 2:3-6
"And I saw the dead, great and small, standing before the throne, and books were opened. Another book was opened, which is the book of life. The dead were judged according to what they had done as recorded in the books." - Revelation 20:12
"For we must all appear before the judgment seat of Christ, that each one may receive what is due him for the things done while in the body, whether good or bad." - 2 Corinthians 5:10
"But because of your stubbornness and your unrepentant heart, you are storing up wrath against yourself for the day of God's wrath, when his righteous judgment will be revealed. God "will give to each person according to what he has done." To those who by persistence in doing good seek glory, honor and immortality, he will give eternal life. But for those who are self-seeking and who reject the truth and follow evil, there will be wrath and anger." - Romans 2:2-8
"Since you call on a Father who judges each man's work impartially, live your lives as strangers here in reverent fear." - 1 Peter 1:17
"For it is not those who hear the law who are righteous in God's sight, but it is those who obey the law who will be declared righteous." - Romans 2:13
"The King will reply, 'I tell you the truth, whatever you did for one of the least of these brothers of mine, you did for me.'" - Matthew 25:40
"Through him and for his name's sake, we received grace and apostleship to call people from among all the Gentiles to the obedience that comes from faith." - Romans 1:5
"Watch out that you do not lose what you have worked for, but that you may be rewarded fully." - 2 John 1:8
"It is impossible for those who have once been enlightened, who have tasted the heavenly gift, who have shared in the Holy Spirit, who have tasted the goodness of the word of God and the powers of the coming age, if they fall away, to be brought back to repentance, because to their loss they are crucifying the Son of God all over again and subjecting him to public disgrace.
Land that drinks in the rain often falling on it and that produces a crop useful to those for whom it is farmed receives the blessing of God. But land that produces thorns and thistles is worthless and is in danger of being cursed. In the end it will be burned." - Hebrews 6:4-8
"First to those in Damascus, then to those in Jerusalem and in all Judea, and to the Gentiles also, I preached that they should repent and turn to God and prove their repentance by their deeds." - Acts 26:20
"Why do you call me, 'Lord, Lord,' and do not do what I say?" - Luke 6:46
"But when you give a banquet, invite the poor, the crippled, the lame, the blind, and you will be blessed. Although they cannot repay you, you will be repaid at the resurrection of the righteous." - Luke 14:13-14
"You are the light of the world. A city on a hill cannot be hidden. Neither do people light a lamp and put it under a bowl. Instead they put it on its stand, and it gives light to everyone in the house. In the same way, let your light shine before men, that they may see your good deeds and praise your Father in heaven." - Luke 5:14-16
Another example that comes to mind is the thief hanging on the cross next to Jesus (Luke 23:32-43). Some argue that it was faith alone (sola fide) that saved him, and in part this is true, but the thief could have retained faith in his heart and done nothing to receive the grace of salvation. It was the fact that the thief spoke out and asked Jesus, "remember me when you come into your kingdom" (verse 42) that he received the gift of salvation. It was faith that enabled him to do so, but faith without showing you have faith is dead faith.
Another example to consider would be the woman who suffered bleeding (Luke 8:43-48); she reached out believing that she would be healed by touching the hem of Jesus' cloak. If she had sat there and done nothing, would she have been healed? Would faith alone been enough to heal her? The woman stepped out in faith in order to be saved. In the same way, good works must come from faith in order for them to be good works.
There is also the matter of Abraham in Genesis 22. God asked that Abraham sacrifice his only son. Abraham went to do so willingly but imagine if he refused! Abraham was able to do so because he had faith, but never did he ask "Lord, is it not enough that I have faith in you?" Abraham's faith is justified when an angel of the Lord stops him from sacrificing Isaac: ""Do not lay a hand on the boy," he said. "Do not do anything to him. Now I know that you fear God, because you have not withheld from me your son, your only son" (verse 12).
For me the kicker is James 2:14-26 (follow link to read).
The common misconception made by anti-Catholics is that we preach "faith OR works". But James 2:14-26 makes strong emphasis that faith alone (sola fide) is inadequate, but works accompanied by faith will save you. Good works must always be performed with faith, as it is faith (grace) that enables us to perform them.
What is most poignant in James 2:14-26 is this:
"You believe that there is one God. Good! Even the demons believe that—and shudder." (verse 19)
"Even the demons believe..." if to have faith is to believe, and if to have faith in Christ is to have believe in Christ, then honestly, as a believer, I sure don't want to be likened to that of a demon!
How do we know faith is real? Faith is real because of what it enables us to do! How do we know if another has faith? Can we see faith? No, but we can see faith put into action, and this is how we know that faith is real and resides within people who have it:
"By their fruits you shall know them. Do men gather grapes of thorns, or figs of thistles?" - Matthew 7:16
In order for faith to be known, it must be manifested; faith alone is never sufficient:
"You are the salt of the earth. But if the salt lose its savour, wherewith shall it be salted? It is good for nothing any more but to be cast out, and to be trodden on by men." - Matthew 5:13
How do you keep the "savour" of salt? How do you keep the light and warmth of faith? By putting it into action, of course; by using it and showing the world that you have it:
"Neither do men light a candle and put it under a bushel, but upon a candlestick, that it may shine to all that are in the house." - Matthew 5:15
Christ wants our faith to shine from the inside out:
"Therefore whosoever heareth these sayings of mine, and doeth them, I will liken him unto a wise man, which built his house upon a rock" - Matthew 7:24
It's one thing to hear the word, but to act on them is something different all together, and this is what Christ instructed us to do.
We do ourselves and each other a great disservice when we do not put into pratice what we have been taught by Christ, as to do so comes from faith. By putting our faith into action we prove the genuineness of our faith. If you have faith, it needs to be demonstrated, else it is dead faith and justifies nothing.