1Jn 2:3,4 We know that we have come to know him if we obey his commands. The man who says, "I know him," but does not do what he commands is a liar, and the truth is not in him.
This is one of the external evidences that one has come to know Christ. Jesus said, "Not everyone who says to me, ‘Lord, Lord,’ will enter the kingdom of heaven, but only he who does the will of my Father who is in heaven." Mt 7:21 In fact referring to Jesus as Lord is not supposed to be simply an acknowledgement of his Diety, but rather it's supposed to imply one's intention of doing what he says. Thus Jesus asks the rhetorical question, "Why do you call me, ‘Lord, Lord,’ and do not do what I say?" Luke 6:46
A person has not come to know Christ, let alone believe in him, if they have simply prayed a prayer to be saved without any actual intention of obeying him. That is not the kind of faith the qualifies one for salvation.