Based on the text, grace is apportioned according to the work that is given to each person.
But to each one of us grace was given according to the measure of
Christ’s gift… 11 And He gave some as apostles, some as prophets, some
as evangelists, some as pastors and teachers, 12 for the equipping of
the saints for the work of ministry, for the building up of the body
of Christ. – Eph 4:7-12
In the world, positions and responsibilities are assigned/awarded according to ability/achievement. In the body of Christ, however, everything is a gift from God, both the work and the grace with which to accomplish it. The measure of the one is directly related to the proportion of the other.
However, since we have gifts that differ according to the grace given
to us, each of us is to use them properly: if prophecy, in proportion
to one’s faith… – Rom 12:6-8
Paul is a perfect example of his own teaching.
For I am the least of the apostles, and not fit to be called an
apostle, because I persecuted the church of God. 10 But by the grace
of God I am what I am, and His grace toward me did not prove vain; but
I labored even more than all of them, yet not I, but the grace of God
with me. – 1 Cor 15:9-10