When Christ entered Jerusalem as King, as prophesied in the Old Testament, the multitudes cried out, quoting Psalms 118.
When John was testifying to the Pharisees and saw Jesus, he proclaimed: “Behold the Lamb of God, which taketh away the sin of the world.”
The leadership of Israel saw the miracles and the fulfilled prophesies that Christ was doing. They knew he was proclaiming to be the Son of God. They had heard John’s witness that he was the Lamb of God. They knew what to do with a lamb on the day of the Passover. They had heard the multitudes quoting scripture.
For their salvation, they only need to continue reading where the multitudes left off:
Psalm 118:26-27 Blessed be he that cometh in the name of the LORD: we have blessed you out of the house of the LORD. 27 God is the LORD, which hath shewed us light: bind the sacrifice with cords, even unto the horns of the altar.