Summary: Some believers seem stuck in spiritual infancy; the author of Hebrews urges them to advance to the "meat" of Christian faith & doctrine and start discipling others.
For a young couple, there’s nothing more wonderful than the birth of a baby. But as much as the parents and grandparents love to hold that bundle of joy, it’s their desire that this little baby grows up to enjoy a full life as a mature adult. God has the same desire for us, His children. That’s why He compels us in Hebrews to “Go on to maturity”. We love it when a baby says “mamma, dada,” but parents would be devastated if their child remained immature.
The author of Hebrews challenges baby-like believers to move from milk to solid food. After church, we’ll have lunch—for most of us, this means grown-up food—not Gerbers! Milk is for beginners; solid food is for the mature. In the Christian life, after awhile we should move beyond the basics and get into the “meat” of God’s word. We’re no longer learning the foundational ABC’s of God’s revelation; we’ve progressed beyond that. But regrettably, some believers who by now ought to be teaching others still need instruction; they’re stuck in spiritual infancy. They’re inexperienced in applying God’s truth to their lives--so much so that they’re in need of having someone sit down with them and go over the basics again. Here’s my point--are we growing, or are we still “baby believers”? Our church’s mission statement indicates that we take spiritual growth seriously: “We proclaim Christ, counseling and instructing all people with all wisdom, so that we may present everyone complete (mature) in Him” (Colossians1:28).
According to the author of Hebrews, we ought to be discipling others; this could mean teaching a Sunday School class or leading a small group Bible study, or by mentoring someone who’s new to the faith. Some parents rely on Sunday School because they’re not equipped to teach their children, and they struggle to answer their kids’ questions about God. We can only lead people as far as we are ourselves.
In II Corinthians we see what’s supposed to occur after initial trust in Jesus: “If anyone is in Christ, they are a new creation; the old life is passing away, and all things are becoming new” (5:17); this process of growth is supervised by the Holy Spirit. But it’s a cooperative effort; we can stunt our own growth if we don’t do our part. Plenty of spiritual food is available, but God’s not about to force-feed us. The last verse of Hebrews 5 (quickview)  says that mature believers “train themselves.” This is sports language, an athletic term referring to physical exercise at a gym. Some sluggish and unskilled believers are in dire need of a spiritual workout!
The writer then in chapter 6 lists 6 foundational truths, what he refers to as the “elementary teachings” of the spiritual life. The first two items, repentance and faith, mark the first steps of salvation. Faith means trusting God, and repentance is a change of mind and a new direction. We turn from sin and self to God, inviting Jesus to be in charge of our lives.