Modern Christians are very much in the "head" faith, mental belief sort of idea of what faith is, preaching the Bible and what "it says" to be believed in, exclusively, even against science. In fact, many absolutely refuse to trust their own hearts. I've known many who even cite scripture to say "don't believe your own heart", absolving themselves of questioning their beliefs, which they should if that is what they conclude from them!
What I see as consistent with "trusting and following God", in those sense of faith and belief, is not a head thing at all.
Rather, it is precisely about the heart, and the heart alone. Trust is a heart thing. Commitment and intention are heart things. The mind can be confused by many beliefs and ideas of what "God wants".
Your view of what faith is, and what it looks like, isn't consistent with what Scripture shows us about what faith is.
First off, you can't have faith without something to first have faith in.
Consequently, faith comes from hearing the message, and the message is heard through the word about Christ
...
How, then, can they call on the one they have not believed in? And how can they believe in the one of whom they have not heard? And how can they hear without someone preaching to them?.
-Romans 10
For since in the wisdom of God the world through its wisdom did not know him, God was pleased through the foolishness of what was preached to save those who believe.
-1 Corinthians 1:21
Also:
-John 5:47
-John 10:38
It doesn't matter if it's God speaking directly to you, an angel delivering the message, or hearing/reading God's word recorded in some form - you can't follow what first hasn't been communicated to you. The disciples heard Jesus speak, they heard voices from Heaven, they heard and saw angels, they saw miracles, they had the OT scriptures to hear and read from. Later believers had the prophetic words, recorded words/deeds of Jesus, OT scriptures, and then writings of the apostles (NT) to put faith in and follow, as well as miracles
Now, you might be able to make a case from some scriptures in Romans that God convicts you in your heart and you deep down know what you're doing is wrong, which is why people who have never even heard the Gospel can be condemned for their sin. Because then you are held accountable for disobeying that feeling, even if you don't know intellectually where that feeling comes from. But ultimately faith is still a matter of obeying what God has communicated to you, and you can't get away from doing that if you aren't aware of God's truth or you refuse to acknowledge it as truth. Everyone is accountable for the truth of God that has been communicated to them, and if you have heard or read God's truth communicated to you then you are accountable for whether or not you choose to put faith in it.
Luke 12:47-48.
Notice how in Jesus's parable that here how even not knowing what you were suppose to do doesn't absolve you from being punished for the sin.
What you feel convinced of in your heart doesn't absolve you of the requirement to follow the truth of God's word that has been revealed to you. God doesn't lie and doesn't change, so he's not going to communicate a truth recorded in the NT and then later tell you something that contradicts that (Galatians 1:8).
Your heart cannot be the sole arbiter in your life or what is true or false because you may not have the willingness or the experience or the understanding to sift out what of your heart is sin vs truth. That's why the Holy Spirit and God's word to us is necessary to guide us into all truth (John 16:13).
And, if God's word being preached to people were not necessary to align them with truth, then Paul would not have said it was necessary in Romans 10. Sending prophets in OT times, or training the apostles in NT times to lead and evangelize, would have been pointless exercises unless it was necessary to help align people's hearts to accept and obey God's truth. In 2 Kings 22, finding a copy of the Scripture that had been lost to them at that time informs the king of things he never knew, moved him to repent, and then changes come about because of it. Prophets speaking to kings had similar effects at times, if they were receptive to hear the truth and willing to act on it. Not all kings were.
Nothing we see in the Bible conveys the idea that salvation comes by merely following your heart, whatever that may be. Two reasons.
1. Because some people have their consciences seared (1 Timothy 4:2) and won't be capable of responding to any conviction in their heart.
2. Their heart is set on wrong ideas and desires. The reason you see many verses in the Bible about deceptive or wicked hearts leading people astray from the truth is precisely why you need God's truth to intervene and set your heart strait:
Jeremiah 22:17, Isaiah 44:20, Proverbs 6:14, Jeremiah 17:9.
That is why we need to rely on God's word through his prophets and apostles, as a trustworthy source communicating what God told them directly, to help us determine what part of our heart is in the truth or mired in deceptive sin. If everyone could equally trust that their hearts were perfectly attuned to discern truth from falsehood then Paul would never have had to rebuke anyone for believing a lie, God would not have had to send prophets to rebuke kings, Jesus would not have to rebuke the Pharisees for telling people lies, Jesus would not have given the great commission to reach the world with the Gospel, and Paul would not have said preachers and teachers were necessary for the sake of the Gospel to spread and for people to be saved by it.
Salvation is always said to come by Faith in God.
Acts 16:1, Hebrews 10:39, Ephesians 2:8 - as a few examples out of many that pervade the NT.
So, since it is established that faith is what leads to salvation, it is necessary that we look more closely at the Bible to understand what faith means and what it actually looks like to be sure we are actually in faith.
To that end, let's look at Hebrews 11, wherein faith is defined as following in obedience to the truth God has communicated.
Hebrews 11 shows us that faith in the truth of what God says, or who He is (actually the two concepts are one in the same, but I digress), is always paired with a corresponding action on the part of the individual that proves they really do have faith in God. In every case they did something to obey God because they trusted Him. That's what faith is.
We also see this concept explained in James 2. He specifically says in verse 14 that faith without corresponding deeds is not a faith that you should expect can save you.
Faith without obedience to God just means you never really had faith to begin with. You can mentally assent to the truth that "Jesus is Lord", but if you never obeyed Him as Lord then you may find yourself having Jesus tell you at the end:
But small is the gate and narrow the road that leads to life, and only a few find it
“Watch out for false prophets. They come to you in sheep’s clothing, but inwardly they are ferocious wolves.
By their fruit you will recognize them. Do people pick grapes from thornbushes, or figs from thistles?
Likewise, every good tree bears good fruit, but a bad tree bears bad fruit.
A good tree cannot bear bad fruit, and a bad tree cannot bear good fruit.
Every tree that does not bear good fruit is cut down and thrown into the fire.
Thus, by their fruit you will recognize them.
“Not everyone who says to me, ‘Lord, Lord,’ will enter the kingdom of heaven, but only the one who does the will of my Father who is in heaven.
Many will say to me on that day, ‘Lord, Lord, did we not prophesy in your name and in your name drive out demons and in your name perform many miracles?’
Then I will tell them plainly, ‘I never knew you. Away from me, you evildoers!’
“Therefore everyone who hears these words of mine and puts them into practice is like a wise man who built his house on the rock.
-Matthew 7
In 1 John 4 we see that acknowleding Jesus as the Son of God means we abide in God, know God, and love.
Linked with that we see above in Matthew 7 that Jesus links knowing Him with being saved from fire. He also links manifesting good fruit and salvation with obedience by referring to them as lawbreakers/evildoers/etc. Good fruit is also known, from John 15, to refer to loving/abiding/obeying God.
In John 15 we see that abiding in God, loving, and obeying God, are all linked together as essentially the same thing because you ultimately can't have one without the other. When God's command is that we love, then obeying Him and loving are inextricably linked together. Which is why in 1 John we see that anyone who doesn't love doesn't actually know or obey God. Further, we see in John 15 that manifesting good fruit is linked with abiding in Jesus - which ties in with what we see in Matthew 7 about how obeying Jesus, knowing Him, manifesting good fruit, salvation are all linked together.
But of all this also ties in with faith as something that is inextricably linked with the concepts of loving, abiding in, and obeying God. Faith is the entry point to it, but not everyone who says they have faith, or thinks they have faith, actually does. You'll only know that by whether or not they manifest fruit consistent with true faith.
The point of drawing out these connections about how different concepts are linked together is to demonstrate why Faith in your own ability to discern the quality of your heart is not enough. You must have faith in what God has said and commanded and pair that faith with action. If you truly believe then you will act in obedience to that truth. But that's where it becomes important that you know what the truth is first. You can't act rightly in concert with truth if you don't accept what God says is true but instead believe in a false truth. A false truth, even if you are faithful to that false truth, will not result in obedience to God. And then you have a problem.
If you don't think you need to abide by God's truth, but you think your own version of truth is sufficient because you feel right about it in your heart, then you put yourself in the position of disobeying God because you are putting your faith in something other than Him and His Word. And since one cannot be saved and be in faith if they are in rebellion to God, you can't say you are in faith if what you put your faith in is a lie that opposes what God has already said is true. Hence, the necessity of making sure what you believe in your heart lines up with what God has already said is true.
If you really believe the gospel is true in your heart, then the fruit of that will be manifest in all these other things like love and obedience. And if you do that then you will be abiding in God, which means you will start acting more in love, which means you know God because God is love.
It's also why Jesus said the real test for a person was the fruit they manifested. Are you obeying God and loving the way he would? Then you have real faith and it has saved you.
Do you claim that you have faith merely because you feel right about what you do and believe in your heart, but your actions don't line up with what God has said you should do and you don't really obey God? Better check what you're really putting your faith in before you end up surprised at the final judgement like the "evildoers" in Matthew 7 were.
There is much more we could bring up as examples, but I believe that should be sufficient to give you an idea of why the Bible has very clear definitions about what it means to be in faith, what results from that, and why your definition of faith is not consistent with what the Bible has outlined.