Note the particular offence on the part of God. It is anger and irritation on account of their unbelief.
If you ask why are people unbelievers, then you see that those without faith never look higher than the earth. Even in the presence of the Son of God and of his wonderful sign miracles, the vast majority of the five thousand fed by Christ looked no higher than one who could provide for their earthly needs (John 6). You can’t believe in what is not in your view at all. They give their lives to things that are passing away, to silly things like bio magnetic bracelets or horoscopes. The evangelist needs to ask people whether they grasp the great gulf between themselves and God, or are they put off from eternal salvation by such small things as the fear of scorn. Are they brainwashed by all the things they believe in taking hold of in this life, things they cannot take with them? Are they addicted to the love of sin which they will choose rather than what God freely offers in the gospel?
‘And they have not known my ways.’ Yes surely that includes the way of holiness and God's commandments, but that's not actually what the text says. They are thinking of the ways of God. We need to learn the ways of God, such as when God brings strength out of weakness. As the apostle Paul says, ‘When I am weak, then am I strong’ (2 Corinthians 12:10); when I am weak in myself, not filled with self-confidence and self-reliance, but strong in dependence upon him, then I am strong. That is God's way. He doesn't mightily bless the strong, he mightily blesses the weak and the humble and the dependent. ‘I think I have many trials’, you may say, ‘and many setbacks.’ Well, we know God's ways, that he will especially prove himself to us and bless us and use us. So we want to know more and more always as life goes on of God's ways.
When we consider the relationship of unbelief to sin, we see that the two are closely connected. Unbelief is like an assistant that stands by the side of sin ready to encourage it and urge it on. When the conscience makes us hesitate, unbelief comes to the aid of sin and says, there are no consequences, no dangers; there is no personal harm that results. Sin is therefore committed, repeated, justified, excused, and glorified in. This shows that unbelief is really the author of all sin.
Can you make yourself believe what you do not believe? Certainly it is our responsibility to believe, for Christ commands it. Nor is it an unreasonable responsibility or something impossible for us to do. The truth is that we put obstacles in the way of our own belief and we refuse to believe, because we see that faith is inconvenient and will take us down a road we do not wish to go down. Every person must cry to God for help when they see this reluctance in themselves to believe, and they must oppose the excuses for unbelief that well up inside them. Faith is the most natural thing for us. It is only when we suppress the evidence that is all around us that we are able to deny that we are created, that we are dependent on God, and that there are tokens of his goodness all around us.