Yes. Romans 10:9 That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved. That means out loud, with your mouth. If you are not able, as in have a physical handicap, your faith, and a thought confession will do. If you are not handicapped, then out loud is the very best way. All Christians are required to testify for the Lord Jesus. Why not start with your confession of faith. That is the very least likely time, if you are in Church, that you will be persecuted for it. You make a verbal confession of faith in front of people who will be glad to hear you do it. That is starting out in your new life drinking milk. Soon enough you will be a meat eating, God lovin testifying machine. Hebrews 5:12 For when for the time ye ought to be teachers, ye have need that one teach you again which be the first principles of the oracles of God; and are become such as have need of milk, and not of strong meat. You must grow in Christ. Paul is rebuking the Jews in this verse because they haven't. They tried to be mature without starting out as babes.New Christians need the milk, mature Christians need the meat. You start something from the beginning, and the beginning of a Christian's testimony is his confession of faith. 1 Corinthians 14:40 Let all things be done decently and in order.

The phrase comes from Rev. 3:20 and is used because in this verse, Jesus uses the metaphor of standing at your door and knocking and tells anyone who hears his voice and "opens the door, I will come in." The phrase is asking people to respond to Jesus' "knock." The answer to your question is a qualified "yes." The metaphor Jesus uses is, after all, a metaphor (does your "life" have a "door"?). It is the excercise of faith in response to the moving of the Spirit that saves. According to Eph. 2:8,9 It is by [God's] grace you are saved through faith. In Acts 16:31 we are told "Believe in the Lord Jesus, and you will be saved," and in John 3:16 "whoever believes in him" will not perish. Jesus told people "your faith has saved you." Evangelical churches generally encourage this response using phrases like "ask the Lord..." to motivate people as an act of will to respond to God's call, or Jesus' knock. Saying words out loud is a good and correct response, but God does not exclude the deaf or mute or even those who respond silently.