Summary: You plant the seeds; God waters. He uses you. It is His Word that accomplishes salvation. It is His gospel that is powerful. It is His Son Jesus who draws. You witness in power when you witness with the Word of God.
"So shall My word be which goes forth from My mouth; it shall not return to Me empty, without accomplishing what I desire, and without succeeding in the matter for which I sent it," (Isaiah 55:11).
Isaiah 55:11 says, "So shall My word be which goes forth from My mouth; it shall not return to Me empty, without accomplishing what I desire, and without succeeding in the matter for which I sent it." God's word is unique. It was by His word (speech) that God created, "God said, ‘Let there be light'; and there was light" (Gen. 1:3). "By faith we understand that the worlds were prepared by the Word of God..." (Heb. 11:3). Jesus is called the Word, "In the beginning was the Word and the Word was with God and the Word was God... and the Word became flesh and dwelt among us..." (John 1:1,14).
When Jesus was on the earth, He taught. He taught with words and His words had a very strong effect on people. They angered some and broke others. But when Jesus spoke, things happened.
Jesus forgave sins by speaking, "And seeing their faith, He said, ‘Friend, your sins are forgiven you'" (Luke 5:20). He raised the dead by speaking, "Lazarus, come forth" (John 11:43). He calmed the wind and sea with words, "Then He arose, and rebuked the winds and the sea; and it became perfectly calm" (Matt. 8:26). He cast out demons by speech, "And He said to them, ‘Begone!' And they came out..." (Matt. 8:32). He healed by speech, "And He stretched out His hand and touched him, saying, ‘I am willing; be cleansed.' And immediately his leprosy was cleansed" (Matt. 8:3,13). God's words are powerful.
The Word (the Bible) is described as having many qualities:
It is inspired: "All scripture is inspired by God and profitable for teaching, for reproof, for correction, for training in righteousness" (2 Tim. 3:16).
It is truth: "The sum of Thy word is truth" (Psalm 119:151).
It makes free: "...If you abide in My word, then you are truly disciples of mine; and you shall know the truth, and the truth shall make you free" (John 8:32).
It produces faith: "So faith comes from hearing, and hearing by the word of Christ" (Rom. 10:17)
It judges: "For the word of God is living and active and sharper than any two-edged sword, and piercing as far as the division of soul and spirit, of both joints and marrow, and able to judge the thoughts and intentions of the heart" (Heb. 4:12).
The Word of God is a mighty weapon. That is why you should memorize!
Rom. 1:16, "For I am not ashamed of the gospel, for it is the power of God for salvation to everyone who believes, to the Jew first and also to the Greek." What is the Gospel? 1 Cor. 15:1-4 says it is the sacrificial death and physical resurrection of Jesus for sins. It is the powerful message of salvation to sinners. If you know that the Word of God will accomplish what God wants it to and if you know that the gospel has power to save, then it should ease your mind to know that in witnessing you are using two very powerful weapons: God's Word and God's Gospel. The Word of God is the Bible. The Gospel of God is His revelation or redemption.
John 12:32, "And I, if I be lifted up from the earth, will draw all men to Myself." Here Jesus speaks specifically about His crucifixion. It is He who draws to Himself all who are to be saved. When you present the gospel (1 Cor. 15:1-4), the sacrificial death and resurrection of Jesus for sins, Jesus draws the sinner to Himself. He does the work, not you.
As a Christian, you are to witness with truth, honesty, and integrity. As the Lord provides the opportunity, you should respond in a humble and gentle spirit (2 Tim. 2:24). And in that, you should point people to Jesus. It is He alone who saves.
If you know that God's Word will accomplish what God desires, that the gospel is powerful to save, and that it is Jesus who draws all men to Himself, then you should realize that the responsibility of salvation does not rest on you, but on God. You are the teacher, the deliverer of good news. "How shall they believe in Him who they have not heard?" (Rom. 10:14). You help them hear!
These three verses should help you to gain confidence. You witness; God saves. You plant the seeds; God waters. He uses you. It is His Word that accomplishes salvation. It is His gospel that is powerful. It is His Son Jesus who draws. You witness in power when you witness with the Word of God.