In Ephesians 4:13, Paul says that Christ gave us the apostles, prophets, evangelists, pastors, and teachers to build up the body of Christ until we attain the "fullness of Christ." Scripture uses the word "fullness" to describe a sense of completeness. So the "fullness of Christ" represents growth into the maturity and wholeness of Christ.
But to really understand what Paul means when he uses this term, let's take a look at how the Bible uses the idea of fullness.
Moses blesses the Israelites
Before Moses's death, he speaks a blessing over the tribes of Israel in Deuteronomy 33. As we grasp what's being said here, it will help us piece together an understanding of the Bible's use of fullness. Moses speaks the following prayer over Joseph (which would cover the tribes of Manasseh and Ephraim):
"May the Lord bless his land
with the precious dew from heaven above
and with the deep waters that lie below;
with the best the sun brings forth
and the finest the moon can yield;
with the choicest gifts of the ancient mountains
and the fruitfulness of the everlasting hills;
with the best gifts of the earth and its fullness
and the favor of him who dwelt in the burning bush.
Let all these rest on the head of Joseph,
on the brow of the prince among his brothers" (Deuteronomy 33:13–16, emphasis added).
Moses's blessing to Joseph's offspring is a prayer for the world to yield the fullness of its fruitfulness. He wants so much more than the world to offer up her gifts to these tribes; he wants to see the world produce all it’s capable of producing.
Fullness in the Book of Romans
Throughout Paul's Epistles, he jumps on this idea of fulfillment to make some vital theological points. He uses the Greek word "plērōma" to describe things coming to completion. The first example happens in Romans 11.
Again I ask: Did they stumble so as to fall beyond recovery? Not at all! Rather, because of their transgression, salvation has come to the Gentiles to make Israel envious. But if their transgression means riches for the world, and their loss means riches for the Gentiles, how much greater riches will their full inclusion bring (Romans 11:11–12, emphasis added)!
Paul is discussing Israel's rejection of Jesus and whether God has abandoned His people. The apostle argues that they haven't transgressed beyond reclamation. In fact, he argues that if Israel hadn't found themselves outside of God's will, then the Gentiles wouldn't have availed themselves of God's salvation.
But Paul seems to point to reconciliation with Israel. The word the NIV translates as "full inclusion" is plērōma. The New King James Version translates it this way:
Now if their fall is riches for the world, and their failure riches for the Gentiles, how much more their fullness (Romans 11:12, NKJV, emphasis added)!
The fullness of the Gentiles
Paul uses this term again as he wraps up his thoughts in Romans 11.
I do not want you to be ignorant of this mystery, brothers and sisters, so that you may not be conceited: Israel has experienced a hardening in part until the full number of the Gentiles has come in, and in this way all Israel will be saved. As it is written:
"The deliverer will come from Zion;
he will turn godlessness away from Jacob.
And this is my covenant with them
when I take away their sins" (Romans 11:25–27).
This time the NIV translates "plērōma" to indicate the full number of the non-Jewish people who will choose to follow Jesus. There is a point when the complete number of those outside of the nation of Israel will have come into the kingdom, and then God will bring the rest of His plan to fruition.
Both uses of fullness here point to the completeness of God’s plan. At some point, God will finish His work at the loom and step back. At that moment, every thread will be accounted for, and the tapestry He has been working on will be seen for what it is: the fullness of His plan. It might not be apparent now, but we will all rejoice in awesome wonder at its conclusion.
The fulfillment of the law
Later, in the same Epistle, Paul addresses an entirely different topic but brings up the same image of fullness. The Greek word for "has fulfilled" is "peplērōken," the perfect active verb tense of "plērōma." When the "fullness" level is at capacity, it has been "fulfilled."
Paul uses this when talking about the relationship between love and the law.
Let no debt remain outstanding, except the continuing debt to love one another, for whoever loves others has fulfilled the law. The commandments, "You shall not commit adultery," "You shall not murder," "You shall not steal," "You shall not covet," and whatever other command there may be, are summed up in this one command: "Love your neighbor as yourself." Love does no harm to a neighbor. Therefore love is the fulfillment of the law (Romans 13:8–10, emphasis added).
Jesus also uses the verb form of "plērōma" in talking about the law. He says:
"Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them. For truly I tell you, until heaven and earth disappear, not the smallest letter, not the least stroke of a pen, will by any means disappear from the Law until everything is accomplished"(Matthew 5:17–18, emphasis added).
What do these two uses of fulfillment have in common? They're both talking about the law being brought to completion. According to the Jews, there was only one way for the law to be fulfilled: it had to be kept. To break one element of the law was to be a lawbreaker.
When Jesus showed up and seemed to discount many first-century best practices for religious leaders, there was some question about the law. Did Jesus think the law should be thrown out? In the Sermon on the Mount, He assures them this not the case.
He hasn't come to overrule the law; He's come to fulfill it. We can think of it as humanity's massive debt. He wasn't going to forgive the debt; He was going to pay it. In that way, the obligation would be fulfilled.
In Romans, Paul argues that love is the fulfillment of the law. When we act in love toward others, we're fulfilling the law. So it makes total sense that when Jesus was crucified, bearing upon Himself the sins of the world, He carried out the greatest act of love, fulfilling the law's requirements.