It is not the theme that is difficult!
It is not in the writer himself! It is certainly not a lack of urgency or importance! The issues are paramount. The whole significance of the Person, Incarnation, Cross and Worth of the Lord Jesus is at stake!
No, the difficulty is in those to whom he writes.
Not that they do not know the Lord. They "have been enlightened"; they had "tasted of the heavenly gift"; had "been made partakers of the Holy Spirit"; had "tasted of the good Word of God"; and "the powers of the age to come"; and yet, and yet, there is an immaturity, a failure to "go on," a spiritual infancy which threatens to be fatal in respect of all the ultimate purposes of their heavenly calling. It is this arrested growth, prolonged babyhood that holds back the spirit and the pen of the Apostle, and would even put restraint upon the Holy Spirit. (See the paragraph mentioned.)
The trouble was seen by their being always occupied with those matters - "principles" - which are meant to be built upon, not toyed with. Perhaps the trouble was deeper than that; it was a dwelling upon the things as such and a failure to discern their real spiritual meaning and implications.
There are two maxims which it will be well for us to have settled quite early. One is that we can only "go on" in the Holy Spirit. The other is that the Holy Spirit can only take us on as the foundations and "principles" are laid and settled.
There are many of the Lord's children who, after many years of being such, are under arrest, paralysed, ineffective, and almost counted out because they are in a state of unsettlement about the "first principles." With some it is a matter of "faith toward God"; with some it is the matter of baptism; with some it is "eternal judgment.'' Let it be clearly recognised that on all such matters the Holy Spirit Himself will demand an absolute settlement and will not take us on to "full growth" until the "principles" are established.
Why are there so many old-aged infants, elderly dependants, spiritual "Peter Pans," amongst the Lord's people? Why is it that after years of work and service so many come to a place where they are beaten and helpless because of being "without understanding" in that sense in which the words are used? Col. 1:9; 1 Cor. 14:20; Matt. 15:16.
It may be - and certainly sometimes is - because at sometime the Spirit's requirement as to some basic principle was unheeded, argued aside, discussed, passed, or definitely refused. That is a sin against the Holy Spirit - while it may not be the sin - and that sin is bound to find us out sooner or later. What we have to say here as we proceed will make clear what we mean by this being found out.
The letter to the Hebrews marks the transition from the fragments of the Prophets to the fulness in Christ, this fulness is spiritual and is consequent upon spiritual revelation which leaves all the "earthlies" behind and comes into the "heavenlies," even in the matter of Divinely constituted institutions, which nevertheless were but as "schoolmaster" to lead to Christ and maturity.
We can still go on with the "things" and stand still as to the "meaning." For instance, it is impossible to have a revelation of the true nature of the Church - the Body of Christ - and remain a denominationalist or sectarian without joining issue with the Holy Spirit.
It is equally impossible to remain a Jew as such (in the matter of Judaism) and be a member of Christ.
Once the Holy Spirit has spoken or enlightened, tremendous crises are reached on foundation principles, and these crises if not settled soon will come up later. The Holy Spirit never moves a fraction from His original premise.
Now, while this is all so important, it but opens up for us the way to a closer consideration of what spiritual maturity is.
There are three letters which deal especially with the matter of unduly delayed maturity, or spiritual childhood continued in too long. They are: "1 Corinthians," "Galatians" and "Hebrews."