C. F. Keil and Franz Delitzsch on 1 Samuel 15:2

1Sa 15:2

“Thus saith the Lord of Zebaoth, I have looked upon what Amalek did to Israel, that it placed itself in his way when he came up out of Egypt” (Exo 17:8). Samuel merely mentions this first outbreak of hostility on the part of Amalek towards the people of Israel, because in this the same disposition was already manifested which now made the people ripe for the judgment of extermination (vid., Exo 17:14). The hostility which they had now displayed, according to 1Sa 15:33, there was no necessity for the prophet to mention particularly, since it was well known to Saul and all Israel. When God looks upon a sin, directs His glance towards it, He must punish it according to His own holiness. This פּקדתּי points at the very outset to the punishment about to be proclaimed.