A. Power comes from the Holy Spirit:

ACT 1:8. But ye shall receive power, after that the Holy Ghost is come upon you: and ye shall be witnesses unto me both in Jerusalem, and in all Judaea, and in Samaria, and unto the uttermost part of the earth.

MIC 3:8. But truly I am full of power by the spirit of the LORD, and of judgment, and of might, to declare unto Jacob his transgression, and to Israel his sin.

JOH 6:63. It is the spirit that quickeneth; the flesh profiteth nothing: the words that I speak unto you, they are spirit, and they are life.

ACT 4:8. Then Peter, filled with the Holy Ghost, said unto them, Ye rulers of the people, and elders of Israel,

ACT 4:13. Now when they saw the boldness of Peter and John, and perceived that they were unlearned and ignorant men, they marvelled; and they took knowledge of them, that they had been with Jesus.

ACT 4:31. And when they had prayed, the place was shaken where they were assembled together; and they were all filled with the Holy Ghost, and they spake the word of God with boldness.

ACT 4:33. And with great power gave the apostles witness of the resurrection of the Lord Jesus: and great grace was upon them all.

1TH 1:5. For our gospel came not unto you in word only, but also in power, and in the Holy Ghost, and in much assurance; as ye know what manner of men we were among you for your sake.

2TI 1:7. For God hath not given us the spirit of fear; but of power, and of love, and of a sound mind.

B. No man can stand up to the power of God's Spirit:

LUK 21:15. For I will give you a mouth and wisdom, which all your adversaries shall not be able to gainsay nor resist.

JER 5:14. Wherefore thus saith the LORD God of hosts, Because ye speak this word, behold, I will make my words in thy mouth fire, and this people wood, and it shall devour them.

ACT 6:10. And they were not able to resist the wisdom and the spirit by which he spake.

2COR 10:4. (For the weapons of our warfare are not carnal, but mighty through God to the pulling down of strong holds;)

C. It has to be by God's power:

1COR 1:18. For the preaching of the cross is to them that perish foolishness; but unto us which are saved it is the power of God.

1COR 2:4. And my speech and my preaching was not with enticing words of man's wisdom, but in demonstration of the Spirit and of power:

1COR 2:5. That your faith should not stand in the wisdom of men, but in the power of God.

1COR 4:20. For the kingdom of God is not in word, but in power.

LUK 4:14. And Jesus returned in the power of the Spirit into Galilee: and there went out a fame of him through all the region round about.

D. God can use you even when you're weak:

GAL 4:13. Ye know how through infirmity of the flesh I preached the gospel unto you at the first.

GAL 4:14. And my temptation which was in my flesh ye despised not, nor rejected; but received me as an angel of God, even as Christ Jesus.

E. God can take over & powerfully use you:

EXO 4:10. And Moses said unto the LORD, O my LORD, I am not eloquent, neither heretofore, nor since thou hast spoken unto thy servant: but I am slow of speech, and of a slow tongue.

EXO 4:11. And the LORD said unto him, Who hath made man's mouth? or who maketh the dumb, or deaf, or the seeing, or the blind? have not I the LORD?

EXO 4:12. Now therefore go, and I will be with thy mouth, and teach thee what thou shalt say.

JER 1:6. Then said I, Ah, Lord GOD! behold, I cannot speak: for I am a child.

JER 1:7. But the LORD said unto me, Say not, I am a child: for thou shalt go to all that I shall send thee, and whatsoever I command thee thou shalt speak.

JER 1:8. Be not afraid of their faces: for I am with thee to deliver thee, saith the LORD.

JER 1:9. Then the LORD put forth his hand, and touched my mouth. And the LORD said unto me, Behold, I have put my words in thy mouth.

MAT 10:20. For it is not ye that speak, but the Spirit of your Father which speaketh in you.

MAR 13:11. But when they shall lead you, and deliver you up, take no thought beforehand what ye shall speak, neither do ye premeditate: but whatsoever shall be given you in that hour, that speak ye: for it is not ye that speak, but the Holy Ghost.

LUK 12:12. For the Holy Ghost shall teach you in the same hour what ye ought to say.

ACT 4:13. Now when they saw the boldness of Peter and John, and perceived that they were unlearned and ignorant men, they marvelled; and they took knowledge of them, that they had been with Jesus.