John 10
37If I am not doing the works of My Father, then do not believe Me.
38But if I am doing them, even though you do not believe Me, believe the works themselves, so that you may know and understand that the Father is in Me, and I am in the Father.”
this is how we can believe and know we are IN Him. we will know -- when we do His works.
Both this point you are making, as well as the standard reply you got from 11, from vs 28-29, must be understood
in context
Jn:28-29 Then they said to Him (Jesus), “What shall we do, that we may work the works of God?” Jesus answered and said unto them,
This is the work of God, that ye believe on him whom he hath sent.
So many people use this passage out of its context. They read Paul's mystery grace revelation into it when that was not the intention of what Jesus was saying above.
John wrote his gospel as a record of the 8 signs that Jesus performed in order for Jews to believe that he is their promised Messiah (John 20:30-31).
In that record,
the signs are seen as works of God. There are at least two times the John account explains that.
John 10:
24 Then came the Jews round about him, and said unto him, How long dost thou make us to doubt? If thou be the Christ, tell us plainly. 25 Jesus answered them, I told you, and ye believed not:
the works that I do in my Father's name, they bear witness of me.
John 14
10 Believest thou not that I am in the Father, and the Father in me? the words that I speak unto you I speak not of myself: but the Father that dwelleth in me, he doeth the works. 11
Believe me that I am in the Father, and the Father in me: or else believe me for the very works' sake. 12 Verily, verily, I say unto you, He that believeth on me,
the works that I do shall he do also; and greater works than these shall he do; because I go unto my Father.
Once you understand what John was trying to do in his gospel, this verse quoted is not saying we are trying to make it say, after we read Paul's revelation of the mystery.
Jesus was not saying to "believe in his death burial and resurrection and that is all you need to do to be saved."
He was telling the Jews to believe in the signs, that he is their promised Messiah. The Jews, and Jesus were always under the Law of Moses pre-cruxifiction, and that Law must still be kept.