Differences between "IEC Standard about Modbus Specification" and "Modbus-IDA about Modbus Specification"?

"IEC Standard about Modbus Specification"

Industrial communication networks - Fieldbus - Communication Profile Family 15: MODBUS®-RTPS This pack contains the following 5 IEC Fieldbus Standards:

IEC 61158-1 Ed 2.0 (2007-11): Industrial communication networks - Fieldbus specifications - Part 1: Overview and guidance for the IEC 61158 and IEC 61784 series

IEC 61158-5-15 Ed 1.0 (2007-12): Industrial communication networks - Fieldbus specifications - Part 5-15: Application layer service definition - Type 15 elements

IEC 61158-6-15 Ed 1.0 (2007-12): Industrial communication networks - Fieldbus specifications - Part 6-15: Application layer protocol specification - Type 15 elements

IEC 61784-2 Ed 1.0 (2007-12): Industrial communication networks - Profiles - Part 2: Additional fieldbus profiles for real-time networks based on ISO/IEC 8802-3

IEC 61918 Ed 1.0 (2007-12): Industrial communication networks - Installation of communication networks in industrial premises

"Modbus-IDA about Modbus Specification"

Modbus Application Protocol Specification V 1.1b
Modbus Over Serial Line Specification And Implementation Guide V1.02
Modbus Messaging On TCP Implementation Guide 1.0b
Object Messaging Specification for the Modbus/TCP Protocol Version 1.1

What are differences between "IEC Standard about Modbus Specification" and "Modbus-IDA about Modbus Specification"?

If I have read the "Modbus-IDA about Modbus Specification",is necessary to read "IEC Standard about Modbus Specification" again?

Any answers will be appreciated.

Thank you