One of my pet hates is when people say to me "your teaching is just too intellectual. Just give us the easy stuff." While I don't doubt that I can be too intellectual, I think what is often meant it "don't stretch me too much."
The writer of Hebrews is pretty clear what he makes of Christians who aren't interested in being stretched in order to go to the next level of their understanding with God. He says that such a lack of diligence with the truths about God reveals infantile faith. He says believers ought to be quick, not slow, to learn.
1. Christians ought to be obsessive about getting as much truth about God as we can, and going as far in our knowledge of God as we can. Else what does it say about our attitude to God? I like what he provides for me but don't want to go any deeper with him? The previous section finished with the world-shattering claim that Jesus has become the source of eternal salvation for those who obey him! Not having a profound desire to know and to grow in him is scarcely Christian
2. He writes to people who should be teachers about God but who aren't because of their lack of diligence to learn from God. This is interesting because it shows that God releases spiritual gifts of teaching in response to desire to learn of him. If you want to be a teacher you have to be a perpetual learner. There are people who ought to be teachers who aren't because of their carelessness. And there are people who have teaching responsibilities who shouldn't because they are careless to carry on growing. Don't listen to teachers who are habitual spiritual infants, regardless of how persuasive they sound, or how big their following
3. The immature can't distinguish good from evil (v14), because that comes from constant practice and reflection on the things of maturity, not the things of infancy
4. The things of infancy he lists fall into three categories: beginning the Christian life (Repentance and faith 6:1), basic church practices (baptism into Christ; laying on of hands in participating with God in the impartation of spiritual gifts and setting people aside for specific kingdom tasks 6:2), teachings about the future (resurrection and eternal judgement 6:2). Note that he thinks these are the basics. If you haven't grasped these, you haven't grasped the basics. And if you have grasped them, you have only grasped the basics. If your church only teaches this, it only teaches the basics. If your church doesn't teach this, then you haven't got the basics
5. The things of maturity with which this is contrasted is the teaching about righteousness (5:13). That is: about having a great high priest, about grace, about justification by faith, about the great exchange which sees us clothed in white as children of the king. It is the teaching about our adoption and status, about the fact that we are saints, about the fact that God's righteousness now determines the whole purpose of our existence - to be for the praise of his glorious grace
Now why on earth would people not want to go on to grasp these latter truths? But often they don't. I come across people who effectively say "I have had my sins forgiven, I am going to heaven, so that's enough. I can now relax and get on with my life." It's like they have ticked the right box on the heavenly insurance application form so that they are covered. But just like any other insurance the policy can now quietly sit in the drawer where they will only refer to it when the need arises.
That is the definition of a stalled Christian. They think they did a one-time only deal with God and life carries on basically as normal. How sad! How much they are missing! And in what danger they stand. The writer to the Hebrews says that not going on to maturity is, in fact, going backwards. There is no neutral gear. A stalled Christian is a Christian going backwards. And a Christian going backwards is always in danger of falling away.
The only way to keep secure from falling away is to keep going forwards. And that means having a desire to press on to maturity.