The word "He" refers to anyone in general. Alternate translation: "Whoever" or "Anyone who" or "The one who" (See: [[rc://en/ta/man/translate/figs-gendernotations]])
Jesus means that when someone welcomes you, it is like welcoming him. Alternate translation: "When someone welcomes you, it is like he is welcoming me" or "If someone welcomes you, it is as if he were welcoming me"
This means that when someone welcomes Jesus, it is like welcoming God. Alternate translation: "When someone welcomes me, it is like he is welcoming God the Father who sent me" or "If someone welcomes me, it is as if he were welcoming God the Father who sent me"