Spiritual maturity is not measured by age or ability but by submission to the Word of God and surrender to the will of God.
The Israelites, redeemed by faith, turned from faith to flesh (that is, self-centered living by trusting in human wisdom, human effort, and human strength), and thus, were not permitted to enter in the Land of Promise, or the life of rest.
By being unwilling to go on to spiritual maturity, that is, living life by faith in Christ, a believer, today, can forfeit, not their salvation, but the abundant life in Christ.
"O come, let us worship and bow down... before the LORD our Maker, for He is our God; and we are the people of His pasture, and the sheep of His Hand. Today if ye will hear His voice, Harden not your heart, as in the provocation... Forty years long was I grieved with this generation, and said, It is a people that do err in their heart... Unto whom I share... that they should not enter into My rest."
"For whatsoever things were written aforetime were written for our learning..."
"Let us go on unto perfection [maturity]."
"I [that is, by God's enablement] press toward the mark [the goal] for the prize [the abundant life of rest in Christ] of the high calling of God [coming to spiritual maturity] in Christ Jesus."
“We are pleased that TBC is offering a number of Jerry Benjamin’s booklets in the Little Nuggets Series. To quote the author, ‘The writings are intended to introduce sinners to the Savior and to refresh and strengthen the spirits of the saints.’ We strongly recommend that these booklets be in every Christian’s devotional library.” —Ruth Hunt
Little Nuggets Series, Booklet #5.