Faith starts from the heart and completes by confession:
”But what does it say? “The word is near you, in your mouth and in your heart” (that is, the word of faith which we preach): that if you confess with your mouth the Lord Jesus and believe in your heart that God has raised Him from the dead, you will be saved. For with the heart one believes unto righteousness, and with the mouth confession is made unto salvation.“ Romans 10:8-10 (NKJV)
We make our spiritual life so personal and secretive and because of that many believe in our hearts but refuse to confess to our friends and relatives. This was my Christian life style in my younger age and I thought that is the very holy way of living and that did not help me or anybody. Then very lately I found I should complete my faith in Jesus by not only believing in my heart but also confessing in my mouth too, to people around, to whom I live and work with. So please understand: our salvation comes to us both by believing in our hearts and confessing with our mouths. Let your hearts be filled with faith and overflow through your mouth effortlessly by the grace of God. Luke 6:45(NKJV)
Faith does not come by reasoning in the brain:
”Now while Paul waited for them at Athens, his spirit was provoked within him when he saw that the city was given over to idols. Therefore he reasoned in the synagogue with the Jews and with the Gentile worshipers, and in the marketplace daily with those who happened to be there. And when they heard of the resurrection of the dead, some mocked, while others said, “We will hear you again on this matter.” So Paul departed from among them. However, some men joined him and believed, among them Dionysius the Areopagite, a woman named Damaris, and others with them.“ Acts 17:16-17, 32-34 (NKJV)
In this passage and in some other places we can see apostle Paul was reasoning with the unbelievers around and he could not make any impact. You can see the result — only some men believed and joined him. This is why we should not discuss or get into any argument while giving the gospel. We should pray for the people around first to allow the Holy Spirit of God to open their hearts and minds to be ready to receive. 2 Corinthians 4:3-4(NKJV). Then ask the Holy Spirit to give you the right words to say with love when there is an opening. 2 Timothy 2:25-26(NKJV). Be ready in the season and out of the season and be watchful and do the work of an evangelist, fulfil your ministry 2 Timothy 4:2-5(NKJV).