“Bear” is not used by Christ in the sense of enduring or tolerating, but in the sense of carrying, as a heavy weight. If something that is very heavy, even though it may be valuable like gold, is laid on the shoulders of a man who is incapable of carrying it, it will crush him rather than bring him blessing and joy. (Maclaren) Revelation from God has a progressive nature to it which is dependent upon our growth in maturity in Christ (1 Cor 3:1; Heb 5:11-14). Their experience had set a limit to their ability to perceive greater truths. God can only reveal as much to a man as he is able to understand. This is not God’s fault, but man’s limitation. We don’t teach a child calculus until he has progressed in knowledge from simple arithmetic, through algebra and geometry, to possess a knowledge base necessary to grasp the fundamental concepts of analytic geometry and calculus. The progressive nature of revelation is not only true in our grasp of things in the physical realm, but also in our grasp of the spiritual. We must receive and use what God has given us before He can or will give us more (Matt 13:12). It takes two things “to make revelation, the light that reveals and the eye that beholds.” (Maclaren)

1 Corinthians 3:1  Brothers, I could not address you as spiritual but as worldly—mere infants in Christ.

Hebrews 5:11-14  We have much to say about this, but it is hard to explain because you are slow to learn.  In fact, though by this time you ought to be teachers, you need someone to teach you the elementary truths of God’s word all over again. You need milk, not solid food!  Anyone who lives on milk, being still an infant, is not acquainted with the teaching about righteousness.  But solid food is for the mature, who by constant use have trained themselves to distinguish good from evil.

Matthew 13:12  Whoever has will be given more, and he will have an abundance. Whoever does not have, even what he has will be taken from him.

This truth helps us to understand why God did some of the things He did in the Old Testament, such as having all of the inhabitants of entire cities killed, even women and children. The Israelites had not progressed to the point where they could understand the importance of purity, sin, and the avoidance of its temptation. They (and we) had to be shown how bad sin really was and is.