[voraa]

function showSection(section){
    for(i=1; i<=5; i++){
        if(section == section){
            // section[i].classList.add('show', 'active');
            console.log(section+[i]);
        } else {
            // section[i].classList.remove('show', 'active');
            console.log(section+[i]);
        }
    }
}

Интересное условие
if(section == section)
Зачем section+[i], а не section+i