Now, there is a sense in which this is true, and a sense in which it isn't.
It is true that "faith" is constantly set over against "works" in the NT because faith is the exact opposite of working for your salvation (Rom. 4:5; Eph. 2:8-10). Faith is looking away from yourself to Christ (John 3:14-16) and resting (Matt. 11:28-30) in His finished work on your behalf (John 19:30) as that which alone can make you right with God. It is compared in Romans 5 to the receiving of a gift (v. 17), the gift of Christ's righteousness. In this sense, believing the Gospel is "easy," in that the person believing ceases to DO anything, and simply gives up, and rests their weight upon Christ. What could be easier than just giving up and resting? What is easier than receiving a gift?
On the other hand, however, faith is also absolutely impossible to the lost man apart from a supernatural work of God. One of the places this is illustrated is in a passage that is often used by those promoting an "easy believism" mentality regarding faith: Romans 10:5-11. But when this passage is seen for what it is, the unbelievably impossible and supernatural nature of saving faith becomes evident.
5For Moses writes that the man who practices the righteousness which is based on law shall live by that righteousness.
6But the righteousness based on faith speaks as follows: "DO NOT SAY IN YOUR HEART, 'WHO WILL ASCEND INTO HEAVEN?' (that is, to bring Christ down),
7or 'WHO WILL DESCEND INTO THE ABYSS?' (that is, to bring Christ up from the dead)."
8But what does it say? "THE WORD IS NEAR YOU, IN YOUR MOUTH AND IN YOUR HEART"--that is, the word of faith which we are preaching,
9that if you confess with your mouth Jesus as Lord, and believe in your heart that God raised Him from the dead, you will be saved;
10for with the heart a person believes, resulting in righteousness, and with the mouth he confesses, resulting in salvation.
11For the Scripture says, "WHOEVER BELIEVES IN HIM WILL NOT BE DISAPPOINTED."
I just want to make one observation from vs. 9 with regards to the content of saving faith. Notice the two things that Paul states are required for a person to believe before they can be saved: 1) Jesus is Lord, and 2) God raised Him (i.e., Jesus) from the dead. Pretty simple, right? What could be easier?
But let's think about this. Take just the first one: "Jesus is Lord." Don't just think about what it says, but think about what it actually means. When someone confesses "Jesus is Lord," what are they really saying? They are saying that a man born two thousand years ago in a small town in an insignificant part of the world, a man who grew up as an uneducated carpenter's son and died the death of a petty criminal, is actually the Creator of everything that exists (John 1:3; Col. 1:16) who is right now seated on the throne of the universe, reigning and ruling (1 Cor. 15:25ff) over every particle of matter that there is. And to top it all off, even though he has never seen Him before with his physical eyes, the Christian believes that this same Jesus is going to come back to earth at the end of time to judge all men (Acts 17:31) and to set up an eternal order of "a new heavens and a new earth" (Rev. 21:1ff)!
When considered in this way, the radical nature of saving faith becomes apparent. How in the world could anyone believe that?! Is it any wonder then, that the gospel always appears as absolute foolishness to the lost man (1 Cor. 1:18ff)? Indeed, as Paul himself says in another place, "no one can say, 'Jesus is Lord,' except by the Holy Spirit" (1 Cor. 12:3).
Now, I do NOT want to give the impression that we shouldn't use passages like Rom. 10 to encourage the lost (and ourselves) to call out to God for mercy and grace; I've used it many times myself, and will continue to do so. But, we must also not give the impression that believing is "easy," in the wrong sense. "Just do this, this and this, and BAM! you're in. Just confess with your mouth and believe in your heart; that's all there is to it!"
Dear reader, that is NOT all there is to it. And if saying "Jesus is Lord" is just a matter of repeating a few words to you, then you need to repent and get right with God. When you cry to Him in truth, you will find that He really is "abounding in riches to all who call upon Him."