Paul was deeply aware that the success of his mission was the Lord's work and not his own.  He said, "I will not venture to speak of anything except what Christ has accomplished through me to bring the Gentiles to obedience--by word and deed, by the power of signs and wonders, by the power of the Spirit of God" (Rom. 15:18-19).  Paul's passion, as always, was to focus all glory on the supremacy of Christ in the mission of the church.  

How did Paul then speak of his own labors?   He said, "By the grace of God I am what I am, and his grace toward me was not in vain.  On the contrary, I worked harder than any of them, though it was not I, but the grace of God that is with me" (1 Cor. 15:10).  Paul worked.  Paul fought the fight and ran the race.  But he did so, as he said in Philippians 2:13, because beneath and within his willing, God was at work to will and to do his good pleasure.  Using a farming image, Paul put it like this:  "I planted, Apollos watered, but God gave the growth.  So neither he who plants nor he who waters is anything, but only God who gives the growth" (1 Cor. 3:6-7).  Paul was jealous to uphold the supremacy of God in the mission of the church.

This jealousy for the glory of God in the mission of the church drove the apostles to minister in a way that would always magnify God and not themselves.  For example, Peter taught the young churches, "Whoever serves [should do so] as one who serves by the strength that God supplies--in order that in everything God may be glorified through Jesus Christ" (1 Peter 4:11; cf. Heb. 13:20-21).  The one who gives the strength gets the glory.  So Peter drove home the absolute necessity of serving in the strength that God supplies and not our own.

Piper, John.  LET THE NATIONS BE GLAD.  Grand Rapids:  Baker Academic.  2007.  pp. 56-57