Had Cain given Abel an idea? We don't know. In any case, Abel follows suit. He turns out to be a thinker. He chooses the firstborn animals. Later, God will prescribe this in the laws of Moses: you must dedicate the firstborn animals to the Lord. Abel senses that. In firstborns you give the whole offspring. You show everything belongs to God. He also gives the best cuts of meat (the fat portions). In later legislation God also makes this a precept: to God you always give the best, nothing that is lame or thin. If you were to give that to a ruler on earth, how would he be offended! You did not have to teach Abel that you also give God, the Most High, the very best.
4 et Abel, de son côté, en fit une des premiers-nés de son troupeau et de leur graisse. L'Eternel porta un regard favorable sur Abel et sur son offrande;