From the pulpit and in his ministry, the pastor must preach the faith. In other words, he is bound by confession and conscience to proclaim the doctrines of the faith in truth and sincerity. If his church subscribes to a confession of faith, such as the Westminster Confession or the Three Forms of Unity, throughout his ministry his teachings need to be consistent with these standards. He must preach the content of the faith. The Jews knew that Paul was preaching the content of the Christian gospel, for they said of him, "He who used to persecute us is now preaching the faith he once tried to destroy" (Gal. 1:23).
Yet that alone is not enough. The preacher must also preach by faith.
For the preacher can stand behind the pulpit fully convinced in his own mind that his message is true. Yet in his heart he can doubt. He can fail to believe that the Lord can truly use his preaching to convert sinners and transform lives. Listen to Charles Spurgeon:
Have faith in the Word of God and in its power to save. Do not go up into the pulpit preaching the truth and saying, ‘I hope some good will come out of it.,’ but confidently believe that it will not return void…Do not speak as if the gospel might have some power or might have none. God sends you to be a miracle-worker, therefore say to the spiritually lame, ‘In the name of Jesus Christ of Nazareth, get up and walk,” and men will rise up and walk.
Indeed, the preacher is to be filled with the Spirit of God and to preach in His power. He is not to trust in his own giftedness or cleverness of speech, but in the presence of Christ in his preaching to change the hearts and lives of his hearers. Preachers are to preach by faith as Spurgeon says, expecting the lame to walk, the blind to see, the deaf to hear, and the dead to rise! With confidence in God blessing the means of preaching He has ordained, they are to call forth these actions with heavenly authority. Paul experienced this in his preaching, for he said, "My speech and my message were not in plausible words of wisdom, but in demonstration of the Spirit and of power" (1 Cor. 2:4).
Pray then for preachers. Ask the Lord to be with them, to grant them His presence and boldness, and to use them to bring the power and glory of His kingdom in this world. Pray that they would not only preach the faith, but preach by faith.
For Spurgeon leaves preachers with some choice words of chastisement if they do not preach by faith, then urges them toward it with a final word of hope.
But if you say, 'I hope dear man, that Jesus Christ may be able to make you rise up and walk,' your Lord will frown on your dishonoring words…(but) if you speak by the Holy Spirit, you cannot speak in vain.