I’d point your friend straight to these sayings of Christ Himself -
‘If you love me YOU WILL KEEP MY COMMANDMENTS’ (John 14:15)
‘Now as He was going out on the road, one came running, knelt before Him, and asked Him, “Good Teacher, what shall I do that I may inherit eternal life?” So Jesus said to him … "you know the commandments: ‘Do not commit adultery,’ ‘Do not murder,’ ‘Do not steal,’ ‘Do not bear false witness,’ ‘Do not defraud,’ ‘Honor your father and your mother.’” And he answered and said to Him, “Teacher, all these things I have kept from my youth.” THEN JESUS, LOOKING AT HIM, LOVED HIM …’ Mark 10:17-21
‘Why do you call me Lord Lord, yet DO NOT DO WHAT I TELL YOU’? (Luke 6:46)
‘Go, therefore, and make disciples of all nations … TEACHING THEM TO DO ALL THAT I HAVE COMMANDED YOU’ (Matt 28:19-20)