God showed up both visually and audibly to the Israelites in Egypt and virtually all of them disbelieved.  God flooded the land with locusts, frogs, and pestilences.  God darkened the sun and killed the firstborn of their captors, but they still questioned all of it—even days later at the Red Sea (Ex. 14:10–12).  The Israelites witnessed the ten plagues, saw the pillars of fire and cloud, watched the parting of the Red Sea, and fed on bread that fell from the sky, yet after all of that, they still couldn't enter the Promised Land because of Unbelief (Heb. 3:16–19).

Some 1,500 years later, God showed up visibly and audibly.  He became a man.  He performed numerous miracles for everyone to see.  Surely His feeding of multitudes with a couple of fish, or His healing countless people of their diseases, or His raising the dead a bunch of times, would have caused people to believe.  Yes, a few did believe, but most did not.  His own people had Him crucified.  They rejected Him.

But how about our generation?  How has God shown Himself?  The ways are too numerous to list try as we might (see here, here, and here), but let's start with this one: no country was ever destroyed, its people dispersed, and then regathered and reestablished, until Israel in 1948.  The Bible said this would happen.  Israel is the national focal point of that old dusty book, and yet here it is after 2,669 years (722 BC to 1948 AD).

Today this stubborn problem of unbelief remains—among both those inside and outside the [visible, institutional] Christian faith.  Sin isn't the problem.  The sin problem was decisively dealt with on the Cross.  The problem that still remains is unbelief.  Non-Christians demonstrate their unbelief through their rejection of Christ.  Many Christians demonstrate their unbelief through rejection of the gospel.  This stubborn unbelief has plagued humanity since Eden when our first parents fell for the lie “did God really say... ?”  Yes, God really did say, and God really does exist, and sin really does have a fatal consequence, and Jesus really is coming back with His garments stained in the blood of His adversaries.

The funny thing about reality is that it's better than anything man could dream up or hope for: God has offered total forgiveness, eternal life, and adoption as His own sons and daughters to anyone from any tribe, nation, or language—apart from any human effort—who merely believes the good news that Christ Jesus came, died for our sins, and rose again.  What is awaiting those who simply believe and accept this most simple of all salvific messages is beyond imagination (1 Cor. 2:9; Rm. 8:18; Ps. 16:11; Jn. 14:1–6; see here, here, and here).  Yet, on the flipside, many won't get any of these things and will even lose what they already have simply because of stubborn pride and unbelief (Mt. 13:12; Jn. 13:18).

To those who are willing to sacrifice that stubborn pride and who will receive the good news like a guileless, believe-anything child, God will speak.  And He'll speak every single day.  Each and every day that believers offer God an open heart, an unstopped ear, and eyes that see, God will speak through His word (2 Tim. 3:16), His Holy Spirit (Jn. 16:13), and through the stars (Gen. 1:14; Ps. 19:1–4).  Are you willing to listen?

God is most certainly speaking and He's speaking every day.  Most will not listen.  When the Day of the Lord arrives, those who have been deaf to His gracious, merciful, still small voice in this present age will be unable to muffle Him when that same voice thunders from Heaven: