The Lord Jesus showed Himself to the Apostle Peter on the Mount of Transfiguration. In 2 Peter, Peter reaffirmed that truth, but then he went on to say that scripture was more sure than that. The apostates challenged or questioned supernatural divine intervention in 2 Peter 3:3-4. Peter's answer wasn't, "No, God still talks to you." He didn't bring that up. If God was still talking to people other than through the written Word of God, what Peter said was superior in 2 Peter 1:19-21, why would he not bring that into the argument? Peter didn't want believers or unbelievers expecting God to talk to them directly. That wasn't going to happen.
In answer to uniformitarianism, a closed system, propagated by the apostates as a basis for rejection of Christ and scripture, Peter gives two types of divine intervention. He doesn't mention God speaking directly to individual believers. He surely would have included that if it were to be expected. Instead, Peter says, scripture (2 Pet 3:2). When he said that "holy men of God spake as they were moved by the Holy Ghost," he was referring to inspiration, such as Genesis, Isaiah, 1 Corinthians, etc., not, "God told me to go to France." God doesn't intervene in that way.
Creation and Conscience
God communicates still through creation to a general audience, what is called "general revelation." God still uses conscience to speak with "the law written in [men's] hearts." Believers are free to be amazed and moved by God's creation, the heavens declaring His glory. They can tap into that multifaceted and complex expression of God's handywork every moment without running out. The conscience can do its part at accusing or excusing, as the Apostle Paul reveals in Romans 2.
The psalmists say a lot about God speaking through creation. The old hymn writers wrote about God's speaking through creation, testifying to the revelation of God to men through creation. Creation isn't enough, but the Apostle Paul relied on it in his preaching on Mars Hill in Athens. An ebb of creation proceeds from the attention on naturalism and uniformitarianism. The founding fathers made their case based upon “the laws of nature and of nature’s God," an emphasis of a vastly different era. The departure from creation brings chaos and confusion to individual, family, church, and government today.
Even though scripture says a lot about conscience and it was very important to the Apostle Paul with all his references to it, I heard very little about it growing up, almost nothing about it in high school, college, or even grad school. I didn't understand the conscience until I was a pastor. I wasn't clueless, but I didn't understand the conscience enough to explain it right. God does speak by means of the conscience through the law of God written in the heart.
The Holy Spirit, God, speaks through scripture. He inspired scripture, but He also continues to speak through it, even as Ephesians 6:17 says that the Word of God is the sword of the Spirit. The Word of God is the instrument of the Holy Spirit. Scripture doesn't say, the voice in your head is the sword of the Spirit. If God speaks in your head with authority, telling you specifics not found in scripture, then Ephesians 6:17 isn't the full truth, thus not the truth.
When Romans 10:17 says that faith comes by the Word of God, it isn't saying that faith comes through a voice in your head. If that were the case, then a basis of faith is not just scripture. If God can tell you to go to France in your head, and you can depend on that as an authority, then it is a basis of faith. If it is God talking, you must believe the voice in your head. You can also be sanctified by a voice in your head as a source of sanctification, even as Jesus said believers are sanctified by the Word of God.
Someone might ask, "What about being led by the Spirit?" What is it to be "led by the Spirit?"
All believers are led by the Spirit of God. Besides Jesus being led by the Spirit into the wilderness for temptation by Satan, the only language of "led by the Spirit" is in Romans 8:4 and Galatians 5:18, which read: "For as many as are led by the Spirit of God, they are the sons of God" and "But if you are led by the Spirit, you are not under the Law." Both of those verses say that if someone is not led by the Spirit of God, he is being led by the world, the flesh, and the devil, and is under the condemnation of the law. There is no middle ground there.
Being led by or of the Spirit is to be characteristically living a righteous life, living a life obedient to the Word of God, to have left the way of doing what one wants for doing what the Holy Spirit desires. I've heard people use the terminology, speaking of the voice in the head, as "following the leading of the Spirit." Following the leading of the Spirit is obedience to the Word of God as a practice or lifestyle moment by moment in one's every day life. It means we're not in charge any more, but the Holy Spirit is. Every time you sin, you are not being led by the Spirit, so that is how you are not led by the Spirit. You were led by something other than the Holy Spirit and the Word of God.
Following the leading of the Spirit isn't hearing a voice in your head that says, "Go to France," so you go to France, because the Holy Spirit told you to go. I've heard people saying that the Holy Spirit led them somewhere and He was doing that leading while that person was disobedient in numerous ways to the Word of God. The leading of the Spirit looks like obedience to the Word of God, not the Holy Spirit telling someone chicken instead of beef.
Perhaps no other means by which God speaks today has been ignored by this generation more than the providence of God. When Peter speaks of the prophets in 2 Peter 3, he also speaks of the fulfillment on earth in history of God's Words. God intervenes in history to fulfill the prophetic texts. Those fulfillments speak.
Providence also speaks through day by day and hour by hour events of the life of a believer. Jesus looks to the providence of God in Matthew 6 when He references the notice of the care of the Lord for the sparrow and the grass of the fields. God is in charge. Men can trust in God. God speaks that message through thousands and hundreds of messages anyone should notice through history and everyday events.
Consider the revelation that is God's providence through the poetry of William Cowper:
God moves in a mysterious way
His wonders to perform;
He plants His footsteps in the sea,
And rides upon the storm.
Deep in unfathomable mines
Of never failing skill
He treasures up His bright designs
And works His sovereign will.
Ye fearful saints, fresh courage take;
The clouds ye so much dread
Are big with mercy and shall break
In blessings on your head.
Judge not the Lord by feeble sense,
But trust Him for His grace;
Behind a frowning providence
He hides a smiling face.
His purposes will ripen fast,
Unfolding every hour;
The bud may have a bitter taste,
But sweet will be the flower.
Blind unbelief is sure to err
And scan His work in vain;
God is His own interpreter,
And He will make it plain.
Paul writes in Romans 2:4 that the "goodness of God leadeth thee to repentance." Men see God's goodness in providence and that leads them to repentance. Micah the prophet wrote (6:9), "Hear the rod." God speaks through judgment and chastisement, messages of His providence. The psalmists said they learned through God's affliction (Psalm 119:71). The entire book of Esther provides a veritable travelogue of God's providence, journeying through many of its sights and sounds.
All of the above are the means by which God still speaks to men today. Even though God speaks through creation, conscience, and providence, His Word still stands as the final arbiter of those three. Any message contradictory to scripture cannot be God speaking. We know they are God speaking, because God says they are when He speaks in His Word. With that being said, men should depend on these and not, due to a kind of idolatrous discontent, upon other unscriptural means, such as a voice heard in one's head, giving instruction outside of the truth of God's Word.