Believing of course extends beyond a confession one day that Jesus is the Son of God, the Lamb that has come to take away the sins of the world and repenting and opening the door of your heart. Believing is an ongoing action word.
Jesus said, "And why do you call me Lord and do not the things that I say?" Luke 6:46
And "If you love me, keep my commandments"
John 14:15
and " He that has my commandments, and keeps them, he it is that loves me: and he that loves me shall be loved of my Father, and I will love him, and will manifest myself to him." John 14:21
What were His commandments?
"Jesus said unto him, Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind. This is the first and great commandment. And the second is like unto it, Thou shalt love thy neighbor as thyself." Matthew 22:37-39
The two commandments Jesus said, are the same as the ten, He just broke them down as after giving them He said "On these two commandments hang all the law and the prophets." Matthew 22:40
"Love the Lord God with all your heart, mind, soul and strength" (first four of the ten) and love your neighbor as yourself." (last six if the ten).
The first one is our vertical relationship with God and the last one is our horizontal relationship with man.
If we believe Him, we will love Him. If we love Him, we will follow Him.
"My Sheep know my voice and I know them, and they follow me."
So, it is a lot more than a prayer one day, or the mouthing of the words, " I believe" if you live until the next day that is, and the next and the next as long as you shall live.
God bless.