A.T. Robertson Commentary Mark 2:14

"And as he passed by, he saw Levi the [son] of Alphaeus sitting at the place of toll, and he saith unto him, Follow me. And he arose and followed him." — Mark 2:14 (ASV)

And as he passed by (κα παραγων). Present participle active, was passing by. Jesus was constantly on the alert for opportunities to do good. An unlikely specimen was Levi (Matthew), son of Alpheus, sitting at the toll-gate (τελωνιον) on the Great West Road from Damascus to the Mediterranean. He was a publican (τελωνης) who collected toll for Herod Antipas. The Jews hated or despised these publicans and classed them with sinners (αμαρτωλο). The challenge of Jesus was sudden and sharp, but Levi (Matthew) was ready to respond at once. He had heard of Jesus and quickly decided. Great decisions are often made on a moment's notice. Levi is a fine object lesson for business men who put off service to Christ to carry on their business.