A. The Word is powerful & convinces people:

2CH 17:9. And they taught in Judah, and had the book of the law of the LORD with them, and went about throughout all the cities of Judah, and taught the people.

LUK 8:5. A sower went out to sow his seed: and as he sowed, some fell by the way side; and it was trodden down, and the fowls of the air devoured it.

LUK 8:11. Now the parable is this: The seed is the word of God.

JOH 4:41. And many more believed because of his own word;

JOH 4:42. And said unto the woman, Now we believe, not because of thy saying: for we have heard him ourselves, and know that this is indeed the Christ, the Saviour of the world.

JOH 5:39. Search the scriptures; for in them ye think ye have eternal life: and they are they which testify of me.

JOH 20:31. But these are written, that ye might believe that Jesus is the Christ, the Son of God; and that believing ye might have life through his name.

ACT 17:2. And Paul, as his manner was, went in unto them, and three sabbath days reasoned with them out of the scriptures,

ACT 17:3. Opening and alleging, that Christ must needs have suffered, and risen again from the dead; and that this Jesus, whom I preach unto you, is Christ.

ACT 18:28. For he mightily convinced the Jews, and that publickly, shewing by the scriptures that Jesus was Christ.

TIT 1:9. Holding fast the faithful word as he hath been taught, that he may be able by sound doctrine both to exhort and to convince the gainsayers.

B. Scripture memorisation is important to witnessing:

PSA 119:42. So shall I have wherewith to answer him that reproacheth me: for I trust in thy word.

PRO 22:17. Bow down thine ear, and hear the words of the wise, and apply thine heart unto my knowledge.

PRO 22:18. For it is a pleasant thing if thou keep them within thee; they shall withal be fitted in thy lips.

PRO 22:19. That thy trust may be in the LORD, I have made known to thee this day, even to thee.

PRO 22:20. Have not I written to thee excellent things in counsels and knowledge,

PRO 22:21. That I might make thee know the certainty of the words of truth; that thou mightest answer the words of truth to them that send unto thee?

MAL 2:6. The law of truth was in his mouth, and iniquity was not found in his lips: he walked with me in peace and equity, and did turn many away from iniquity.

MAT 12:34. O generation of vipers, how can ye, being evil, speak good things? for out of the abundance of the heart the mouth speaketh.

MAT 12:35. A good man out of the good treasure of the heart bringeth forth good things: and an evil man out of the evil treasure bringeth forth evil things.

ACT 13:32. And we declare unto you glad tidings, how that the promise which was made unto the fathers,

ACT 13:33. God hath fulfilled the same unto us their children, in that he hath raised up Jesus again; as it is also written in the second psalm, Thou art my Son, this day have I begotten thee.

ACT 13:34. And as concerning that he raised him up from the dead, now no more to return to corruption, he said on this wise, I will give you the sure mercies of David.

ACT 13:35. Wherefore he saith also in another psalm, Thou shalt not suffer thine Holy One to see corruption.

2TIM 4:2. Preach the word; be instant in season, out of season; reprove, rebuke, exhort with all longsuffering and doctrine.