Explanation

The meaning in a few plain lines

The Prophet (may Allah's peace and blessings be upon him) informed that whoever says upon hearing the muezzin: "I bear witness that there is no god but Allah alone without any partner," i.e., I acknowledge, confess, and say that there is no deity truly worthy of worship except Allah, and all other deities are false. "And that Muhammad is His slave and messenger," i.e., he is a slave who should not be worshipped and a messenger who does not lie. "I am pleased with Allah as a Lord," i.e., with his Lordship, divinity, names, and attributes. "With Muhammad as a messenger," i.e., with everything he was sent with and conveyed to us. "And with Islam," i.e., with all the rulings of Islam including the commands and prohibitions, "as a religion," i.e., by way of belief and submission. "His sins will be forgiven," i.e., the minor sins.