[For] “everyone who calls on the name of the Lord will be saved.” 14 How then will they call on him in whom they have not believed? And how are they to believe in him of whom they have never heard? And how are they to hear without someone preaching? [15 And how are they to preach unless they are sent? As it is written, “How beautiful are the feet of those who preach the good news!”] —Romans 10:13-14 
It never ceases to amaze me that the angel of the Lord asks Philip to assist the Ethiopian who was coming back from Jerusalem reading the Scriptures. Was there really a need for Philip to intervene when the Bible says that the Word of God is enough to bring forth men from the deepest darkness (Psalm 19:8b)? Why did a man, even more prepared than Philip, need help to understand? Why did the angel not come, but instead call a sinful man to explain the Word?
It is true that Philip comes, and when he hears the Ethiopian reading in Isaiah, he asks: "Do you understand what you are reading?” To which the man answers, “How can I, unless someone guides me?" He then "invited Philip to come up and sit with him” (Acts 8:29-31).
That Ethiopian official asked a stranger to tell him about the One to whom the prophecy referred, and Philip told him the gospel of Jesus (Acts 8:35). The result was wonderful—a heart of stone transformed into a heart of flesh.
Still, wasn’t the Bible enough for his conversion? Couldn’t the angel be the messenger to bring the good news? There was at least one precedent in Luke 2:11. I think our best conclusion is that God is being consistent with what the apostle Paul would say some years later, That "…it pleased God to save the believers by the folly of preaching” (1 Corinthians 1:21b).
Salvation is a gift from God, but so is every detail involved in the process that will culminate in a new life. And He does it in such a way that glory can only fall upon Him. God calls, empowers, and puts a spark in the hearts of weak men who will open their lips as heralds to speak to the ears that God Himself has prepared for them to react favorably to the gospel. These hearts confess to all men that Jesus is Lord and Savior of their lives. See why it cannot fail?
Brethren, let us pray intensely, not only that the Word of God may be known in every corner of the earth, but for those whom He sends—and those whom He will send—for the hearts that are waiting. It is not that the natural man seeks God, but we remember Jesus when He tells us that the fields are ready for the harvest—and so we pray earnestly that the Lord of the harvest will send forth laborers into His harvest (John 4:35, Mathew 9:38).
Israel looked forward to this time. We have the privilege of living it (Isaiah 52). Rejoice and give glory to God for those who proclaim the Gospel.
How does the reality of God’s intervention in each phase of His work affect your prayer life?