Have you watched workers clear an area where a building is going to be located? You probably noticed they first made it level, then dug a trench for a foundation, and finally poured in concrete on which to build the walls.
A building needs a good foundation so it will not slide on the dirt under it. A good foundation is always built first for without it a building is never safe (cf. 1 Corinthians 3:11). Yet if the workers stopped after making the foundation there would just be a level area with some concrete. While some things could be done on a concrete foundation, a person would not be safe from a storm there. A person could not come in from the cold there.
What if the workers started building another foundation on top of the old one? In New Testament times God had to tell some Christians to not stop with the foundation of the Old Testament teachings. He wanted them to build Christ's house, the church, on that foundation, but then to go on. Therefore leaving the principles of the doctrine of Christ, let us go on unto perfection; not laying against the foundation of repentance from dead works, and of faith toward God (Hebrews 6:1).
The same principle holds for us today. We cannot stop with learning just the simple things from God‘s Word (Hebrews 5:12-14). We must continue to build on our foundation and build a beautiful Christian life (2 Peter 1:5-8). We must build up the church each day for it is the one place we find safety from the storms of life and warmth from the coldness of sin in the world (Ephesians 2).
And whosoever doth not bear his cross, and come after me, cannot be my disciple. For which of you, intending to build a tower, sitteth not down first, and counteth the cost, whether he have sufficient to finish it? Lest haply, after he hath laid the foundation, and is not able to finish it, all that behold it begin to mock him, saying, This man began to build, and was not able to finish - Luke 14:27-30