44 How can you believe, when you receive glory from one another and you do not seek the glory that is from the one and only God? (John 5:44)
The “belief” Jesus referred to must certainly have been deeper than a surface-level belief, since satan and the demons also have belief at some level……
19 You believe that God is one. You do well; the demons also believe, and shudder.
The demons believe that God, Jesus, and the Spirit exist (God is One), and are well aware of His power and their ultimate judgement at His hands (the reason for their shuddering). But, in their rebellion against God they rejected His right to rule over them.
That is why real, genuine, sincere saving “belief” goes beyond a mental acknowledgement of God and Jesus, all the way to a true inward and outward acknowledgement of His personal Lordship.
One illustrative image would be that of a medieval duke kissing the ring of the king to acknowledge his kingship, or a mob under-boss kissing the ring of the organization head to publicly pay homage. This public acknowledgement is spoken of several times…
9 that if you confess with your mouth Jesus as Lord, and believe in your heart that God raised Him from the dead, you will be saved;
1 John 4:15
15 Whoever confesses that Jesus is the Son of God, God abides in him, and he in God.