There are three lines of truth that run throughout the scripture. They are (1) salvation truth, (2) church truth, and (3) kingdom truth. All these truths must be distinguished from one another or otherwise you can become confused. Last week we started out giving the introduction to the subject of Hermeneutics which is the science of Biblical interpretation. The Bible says in II Timothy to rightly divide the word of truth. If you don't, then there will be much doctrinal confusion.
Salvation truth is manifested throughout the scriptures from Genesis to Revelation. There has always been only one way to save sinners and that's through the cross of Calvary. Everything that man did in the Old Testament, they always looked forward to Calvary in faith. There has never been any other method of salvation than through Calvary. Hebrews 9:26 "For then must he often have suffered since the foundation of the world; but now once in the end of the world hath he appeared to put away sin by the sacrifice of himself." I Peter 1:20 "Who verily was foreordained before the foundation of the world, but was manifest in these last times for you."
Church truth is only found in the New Testament and is found primarily in the Pauline Epistles. The church is a hidden mystery in the Old Testament. The Old Testament believers didn't see what we see. They knew nothing of the church.
Just as salvation truth is run throughout the Bible, so is kingdom truth. God has always had the intention to set up his kingdom in this world one of these days. The Psalms are full of kingdom truth. So are many of the Lord's parables.