"But to each one of us grace has been given as Christ apportioned it." NIV translation
Each and every one of us must fall back on grace because we all have sinned and grace is the only cure. No matter how many sins you have committed or how few it seems someone else has done, God's grace covers them both.
"This is why it says: 'When he ascended on high, he led captives in his train and gave gifts to men.' (What does 'he ascended' mean except that he also descended to the lower, earthly regions? He who descended is the very one who ascended higher than all the heavens, in order to fill the whole universe.)" NIV translation
Paul quotes Psalm 68:18 which is about the exodus of God's people from captivity in Egypt as well as our escape from the captivity of sin. This passage also speaks to the fact that, when Jesus died on the cross, he went to share the gospel with those people who had died yet not heard the good news.
"It was he who gave some to be apostles, some to be prophets, some to be evangelists, and some to be pastors and teachers," NIV translation
We see here that no true calling originates with the will of man but only through the will of God. Those that God calls He also equips for the work. These days we have gotten away from the calling of God and instead taught people that they can go to a college to get prepared to do these things. A college can be a tool that God uses but it is still only God that can call and equip you for the ministry He has laid out for your life.
"to prepare God's people for works of service, so that the body of Christ may be built up until we all reach unity in the faith and in the knowledge of the Son of God and become mature, attaining to the whole measure of the fullness of Christ." NIV translation
No matter what the gifts are that God has given you, they are all given for the same purpose which is growth. God provides many resources (even this website) to help his children grow to be mature and productive. We have to acknowledge the fact that none of us are completely mature yet and we do not fully understand what we have in Jesus Christ.