How is the word made effectual to salvation?

Answer

The Spirit of God maketh the reading, but especially the preaching of the word, an effectual means of convincing and converting sinners, and of building them up in holiness and comfort through faith unto salvation (; ; ; ; ; ; ; ; ).

Read the 9 proof texts (KJV)

Nehemiah 8:8: So they read in the book in the law of God distinctly, and gave the sense, and caused [them] to understand the reading.
Acts 26:18: To open their eyes, [and] to turn [them] from darkness to light, and [from] the power of Satan unto God, that they may receive forgiveness of sins, and inheritance among them which are sanctified by faith that is in me.
Psalm 19:8: The statutes of the LORD [are] right, rejoicing the heart: the commandment of the LORD [is] pure, enlightening the eyes.
Acts 20:32: And now, brethren, I commend you to God, and to the word of his grace, which is able to build you up, and to give you an inheritance among all them which are sanctified.
Romans 1:15-16: ¹⁵So, as much as in me is, I am ready to preach the gospel to you that are at Rome also. ¹⁶For I am not ashamed of the gospel of Christ: for it is the power of God unto salvation to every one that believeth; to the Jew first, and also to the Greek.
Romans 10:13-17: ¹³For whosoever shall call upon the name of the Lord shall be saved. ¹⁴How then shall they call on him in whom they have not believed? and how shall they believe in him of whom they have not heard? and how shall they hear without a preacher? ¹⁵And how shall they preach, except they be sent? as it is written, How beautiful are the feet of them that preach the gospel of peace, and bring glad tidings of good things! ¹⁶But they have not all obeyed the gospel. For Esaias saith, Lord, who hath believed our report? ¹⁷So then faith cometh by hearing, and hearing by the word of God.
Romans 15:4: For whatsoever things were written aforetime were written for our learning, that we through patience and comfort of the scriptures might have hope.
1 Corinthians 14:24-25: ²⁴But if all prophesy, and there come in one that believeth not, or one unlearned, he is convinced of all, he is judged of all: ²⁵And thus are the secrets of his heart made manifest; and so falling down on his face he will worship God, and report that God is in you of a truth.
2 Timothy 3:15-17: ¹⁵And that from a child thou hast known the holy scriptures, which are able to make thee wise unto salvation through faith which is in Christ Jesus. ¹⁶All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness: ¹⁷That the man of God may be perfect, throughly furnished unto all good works.