Although it was the Lord's will that there be a united Church, He knew that it would not happen. In Matthew Thirteen, the Parables of Jesus clearly reveal that the Church would be as we see it today. In verse 24-30, Jesus describes the Church as being infiltrated by "agents of Satan" or "tares." Since the modus oporandi of Satan is to steal, kill, and destroy (Jn. 10:10), it is not surprising that there would be much discord among the brethren (Prov. 6:12-19).
In verses 31-32, Jesus speaks of the Church being like a tiny seed, and growing into such a large tree that "the birds of the air" make their nests in it. "Birds" in the parables of the Lord also represent the "agents of Satan" (compare 3:4 w/ 3:19). When we think of a tree, we usually think of a single trunk rising from the ground, the top of which has many branches. So it is with the Church.
Again, in the Parable of the Leaven, the true bread is corrupted by leaven (yeast). Leaven gives the bread the appearance of containing a large amount of substance, but within lie thousands of pockets of "air." Leaven always represents evil in the Scriptures (Mt. 16:5-12; 1 Cor. 5:8). The Feast of Pentecost (Wave Loaves - Lev. 23:15-20) represents the Church Age, with the Church being made up of both Jews and Gentiles (Greeks), neither being sinless (Gal. 3:28; Col. 3:11; 1 Jn. 1:8-10).
The Church cannot be perfect; it is made up of imperfect people?