This is a question that every Christian wonders about at some point. What about people who haven’t heard of Jesus? Does God hold them responsible for rejecting Jesus? Why are they guilty?
This question is answered in Romans 1:18-20. “The wrath of God is being revealed from heaven against all the godlessness and wickedness of people who suppress the truth by their wickedness, since what may be known about God is plain to them. For since the creation of the world God’s invisible qualities – his eternal power and divine nature – have been clearly seen, being understood from what has been made, so that people are without excuse.”
Every person, no matter whether they have heard about Jesus or not, knows enough about God to respond to him appropriately.
Everyone who looks the beauty of the world, the immensity of the universe, the detail of the carefully designed creatures and systems, who feels the tug of conscience, or experiences a yearning in the heart for justice or love, can truly know something about God. He is revealed in these things, and in many more.
So people are without the excuse that they do not know God.
More than that, for people who have been raised believing in other gods, they have every opportunity to recognise the fact that these are not true. That they are inconsistent, or clearly nonsense, or a scam.
And because people do not respond to what they know of God, even if they only know a little, God is perfectly justified in holding them accountable for their sin in not responding to him.
Recognising God from creation is, of course, not sufficient for salvation. Jesus said he is the only way to God (John 14:6). He also said that anyone who seeks him will find him (Mathew 7:7-8). I have met people from non-Christian backgrounds, in countries where Christianity is banned, who have had Jesus reveal himself to them because they have sought God. They have had dreams, and messages, which point them to Jesus, so they can be saved from the judgement they deserve by putting their trust in him.
Anyone who says that they don’t see any evidence for God, or refuse to accept that God is revealing himself to them, is deceiving themselves, which is both sad and terrible at the same time. We should pray that God will open their eyes and their hearts to comprehend and respond to what they know, and that they will have the gospel of Jesus proclaimed to them clearly (which might be a job for you to take part in!).