Q. Why doesn't everyone respond positively to the Gospel?
A. First, I will recommend our TULIP series of books that explain about man's depravity and God's election (click here to go to a page that lists these publications). Quite simply, the Bible always classifies people into two groups: 1) God's elect who respond to the Gospel with saving faith; and 2) all the rest who either yawn it off, get a bit upset, or even get into a murderous rage.
Notice Acts 9:22: "But Saul increased the more in strength, and confounded the Jews which dwelt at Damascus, proving that this is very Christ." This was shortly after Saul's conversion. At first, this verse might not seem relevant to this question. That's because the relevance only comes out in the Greek. The word "confounded" is translated from sunechunnen. This word means to pour or throw together, but in confusion. The Greek word that "proving" is translated from is sunbibazōn. It means to join together compactly and neatly; to knit together. In this case, it would mean to carefully lay down a tight, logical argument.
Thus, what is happening in this verse, what really comes out in the Greek, is that the more Saul made a neat, logical argument to prove that Jesus is the Christ, the more he threw the Jews into confusion. This shows the utter unwillingness of these Jews—in fact, their inability—to accept the logical argument Paul was inspired by the Holy Spirit to teach. Then, in the next verse, we read, "And after that many days were fulfilled, the Jews took counsel to kill him."
Paul was evangelizing with a carefully laid out, neatly compacted, logical, biblically founded argument. You would think any rational person would at least give careful consideration to it. But these people acted irrationally. Paul's message so confused them that they wound up plotting to kill him.
Paul writes about this kind of reaction in 1 Corinthians 1:18: "For the preaching of the cross is to them that perish foolishness; but unto us which are saved it is the power of God." Likely, anyone who is a faithful preacher of the Gospel has experienced this phenomenon. When you preach the Gospel—the liberating truth of God's sovereign grace and His free gift and Jesus' fulfillment of the law—there are those for whom the light goes on and they are as sheep hearing their Master's voice in what you say (see John 10:4-5, 16). And then there are those who are thrown into confusion and, for some, even murderous rage (see Acts 7:54; Luke 6:11).
Again, Paul says, "To the one we are the savour of death unto death; and to the other the savour of life unto life. And who is sufficient for these things?" (2 Corinthians 2:16). Yes, this is the way it is for anyone who teaches from the Scriptures faithfully. Paul continues in 2 Corinthians 2:17: "For we are not as many, which corrupt the word of God: but as of sincerity, but as of God, in the sight of God speak we in Christ." If you are not as the many who corrupt the Word of God, you will suffer persecution: "Persecutions, afflictions, which came unto me at Antioch, at Iconium, at Lystra; what persecutions I endured: but out of them all the Lord delivered me. Yea, and all that will live godly in Christ Jesus shall suffer persecution. But evil men and seducers shall wax worse and worse, deceiving, and being deceived. But continue thou in the things which thou hast learned and hast been assured of, knowing of whom thou hast learned them" (2 Timothy 3:11-14). God gives the grace to believe to whom He will (Romans 9:18).
The Gospel "is the power of God unto salvation to every one that believeth" and we must not be ashamed of it (Romans 1:16). But we must also expect that many will not respond positively to it. In fact, some will be hostile. No matter how beautifully, perfectly, or forcefully the Gospel is presented, the reprobate will hate and reject it. No matter how poorly or feebly the Gospel is presented, the elect will receive it with joy and grow in grace and knowledge. This is the Lord's doing, and it is marvelous in our sight (Mark 12:11).