One reason many give for not believing the gospel or the true message of scripture is the quality of the supportive evidence. In their assessment, the means by which God persuades of His existence or of the truth of the gospel does not rise to a high enough caliber to believe. The Bible preemptively strikes at this excuse by informing us that men already know God and they suppress the truth in their unrighteousness (Romans 1:18). In other words, men have a will problem and not an intellect problem. This is why scripture is the solution, because the will requires a supernatural work to change. The Bible is the instrument of the transformation of the will, necessary for true salvation.
There are mounds of evidence, more than enough. God says there is enough (Romans 1, Psalm 19). However, I understand the criticism. God is all-powerful. If He wants us to believe in Him, and He can do anything that He wants, then why wouldn't He just provide a crown performance to every single person who ever lived? Furthermore, why should anyone even be required to believe in Him, when He could just show Himself directly to everyone?
I use the term, crown performance, in line with what an entertainer does for a king or queen, except in reverse. The traveling minstrel comes to the throne room and entertains the king or queen to a thumbs up or thumbs down. In this case, God comes to a person and performs for him, jumps through the person's hoops, to prove to the person who God is. God doesn't do this, because God wears the crown. We perform for Him, not Him for us.
God gives sufficient evidence for the one who seeks Him. You may say or think, "But we can't seek Him." We can't on our own, but God enables everyone to seek Him through His powerful revelation (Romans 10:17). Men do not believe in Him because of a lack of knowledge, but because of a suppression of that knowledge. In other words, men don't seek God while He may be found (Isaiah 55:6). Jesus said they don't strive (agonize) to enter the narrow gate (Luke 13:24).
Man on his own does not seek after God. With God's revelation, man can seek after God. God wants man to seek Him. He must receive what he knows and upon receiving that, he receives more, until he finally receives enough. This pleases God. The idea that men need more evidence does not please God. It's rebellion against God. It isn't thankful for what God has given.
What I'm writing takes away the pressure off the evangelist. The evangelist offers the gospel. The gospel is great. There's nothing better. If someone doesn't want the gospel, there isn't anything more that the evangelist can do.
God calls every believer to preach the gospel. In that way, God intends every believer to be an evangelist, which is a person who preaches the gospel. There is the office of the evangelist too, but there is the general job of preaching the gospel, which is to be an evangelist. The message of the gospel itself is the allure of the preaching of the gospel. No one can offer something greater, so that if someone doesn't want it, he's not going to be persuaded by something other than the gospel, which proclaims the goodness of God.
God isn't going to provide a crown performance, so for those for whom the evidence God gives isn't enough, they're not going to believe. God has given sufficient evidence to believe through general revelation (creation, conscience, providence, etc.) and special revelation (the Bible). If someone doesn't get saved, it's not because of the knowledge, but because of rebellion.