Why do people have to pray to accept Christ if salvation is by faith in Christ alone?

The issue of praying to receive Christ is more a matter of helping a person grasp that which he or she needs to do or has done in trusting the Savior. It is true that if a person truly trusts in the person of Christ as their Savior, then they are born into the family of God, indwelt by the Spirit, regenerated, and all the rest. Prayer, however, is one of God means of grace whereby we may express our desire to enter into fellowship with Him as a child. It is the avenue He offers us of expressing our faith. Further, note what Romans 10:8-13 says:

But what does it say? “The word is near you, in your mouth and in your heart” (that is, the word of faith that we preach); 9 because if you confess with your mouth that Jesus is Lord and believe in your heart that God raised him from the dead, you will be saved. 10 For with the heart one believes and thus has a right standing and with the mouth one confesses and thus has salvation. 11 For the Scripture says, “Whoever believes in Him will not be disappointed.” 12 For there is no distinction between Jew and Greek; for the same Lord is Lord of all, abounding in riches for all who call upon Him; 13 for “Whoever will call upon the name of the Lord will be saved.”

The word “confess” means to acknowledge or agree. It often involves what is expressed with the mouth (as the passage says) or at least with the mind. In the context, this passage is not talking about a public confession as many claim, but simply the means of expressing one’s faith to God. Note the statement in verse 13, “whoever will call upon the name of the Lord will be saved.” It can be put this way:

10:9-13. In these verses Paul states the content of that message concerning faith. Confessing with the mouth that Jesus is Lord is mentioned first to conform to the order of the quotation from Deuteronomy 30:14 in Romans 10:8. The confession is a personal acknowledgement that God has been incarnated in Jesus (cf. v. 6), that Jesus Christ is God. Also essential is heart-faith that God raised Him from the dead (cf. v. 7). The result is salvation. The true order is given in verse 10: For it is with your heart that you believe and are justified (lit., “it is believed unto righteousness”), and it is with your mouth that you confess and are saved (lit., “it is confessed unto salvation”). Yet these are not two separate steps to salvation. They are chronologically together. Salvation comes through acknowledging to God that Christ is God and believing in Him. In other words, Confession with the mouth and belief in the heart refer to the believer’s outward and inward responses. His inward conviction finds outward expression in a prayer of faith to God, not as a work for salvation, but as an expression of faith, which may also give comfort and assurance to the new Christian.