ਜੇ ਸਭ ਕੁਝ ਰੱਬ ਦੀ ਮਰਜ਼ੀ ਨਾਲ ਹੋ ਰਿਹਾ ਹੈ ਤਾਂ ਪਾਪ ਵੀ ਕਿਉਂ ਨਹੀਂ ਸ਼ਾਮਲ?

Let us first understand what Hukam ਹੁਕਮ means then the meaning of the verse will become clear.
ਹੁਕਮ command is the spiritual, material and physical phenomena we are subject to; the ਕਰਤਾ doer has set up these phenomena which pervade and are sort of the “pulse and liveblood of” the creation. GOD is involved in the goings-on in the creation. Some of these goings-on occur as fixed physical phenomena e.g. the phenomena that keep the planets in their motion, gravitation etc (passive phenomena that do not change) and others are by active involvement of God e.g. the occurrence of a volcanic eruption etc. It is important to understand that ਹੁਕਮ command not only encompases the physical phenomena (ਸਰਗੁਣ) but also the spiritual (ਨਿਰਗੁਣ/ ਸਰਗੁਣ) aspect of the creation as well as the time dimension. As an example of physical phenomenon, if we step beyond the ledge of a multi-story building we are going to go downwards i.e. fall and get hurt or even killed. It is because of the physical law (ਹੁਕਮ command) that we do not just stay put in the air beyond the ledge or go upwards. This physical phenomenon, science calls ‘gravitation’, is ਹੁਕਮ command. By these phenomena we live on this earth and it is by these phenomena that we are happy (heaven) when we live in-synchrony with Hukam and we suffer (hell) when we live out-of-synchrony with Hukam. Similarly, the entire creation acts in synchrony with these phenomena ਹੁਕਮ Command.

The key points relating to ਹੁਕਮ command are as follows.
• Before creation was started, God’s ਹੁਕਮ command existed.
• God’s ਹੁਕਮ command is perfect.
• The creation, of which the earth, land, water, sky, fire, woods, meadows, seasons is a part of, was created through ਹੁਕਮ command and it operates within the bound of ਹੁਕਮ command since ਹੁਕਮ command pervades the creation. It is through ਹੁਕਮ command that the preservation (ਪਾਲਨਾ) of the creation is taking place.
• The creation (including earth) will eventually come to an end through ਹੁਕਮ command.
• Maya was created through and within ਹੁਕਮ command. Brahma, Vishnu and Siva are a part of Maya and abide by ਹੁਕਮ command.
• Through ਹੁਕਮ command, souls, human beings are created, be born and die (the metaphorical “messenger of death” (ਜੰਮ ਜੰਦਾਰ) being a part of ਹੁਕਮ command) and are subject to reincarnation according to karam.
• It through ਹੁਕਮ command that one attains status in society, high or low, success or failure, fame and infamy and other worldly aspects of life. These are based on our past deeds ਕਰਮ karma.
• The ਮਨ mind has the possibility to make its own decisions (in Antahkaran) but within the constrains of ਹੁਕਮ Hukam. Therefore, we are responsible for our actions and will face the consequences.
• The extent of ਹੁਕਮ command is limitless and cannot be known.
• GOD’s ਹੁਕਮ command is realised through the teaching of Gurbani.
• One who does not abide by and hence realise ਹੁਕਮ command is a ਮਨਮੁਖ manmukh, ruled by the five evils i.e. natural instincts of ਕਾਮ, ਕਰੋਧ, ਲੋਭ, ਮੋਹ, ਹੰਕਾਰ lust, anger, greed, attachment, ego always indulging in Maya as a “want” not a “need”. This will subject the person to non-beneficial happenings, examples are wondering around lost, having fickle consciousness, subject to stress and pain, and hence devoid of inner peace. These natural instincts are necessary for our survival. However, there is a need to have a good understanding of the 5 evils; why they are necessary and when do they become evils – this boils down to the words NEED and WANTS.
• Realisation of ਹੁਕਮ command leads to the suppression of our five evils i.e. natural instincts of ਕਾਮ, ਕਰੋਧ, ਲੋਭ, ਮੋਹ, ਹੰਕਾਰ lust, anger, greed, attachment, ego; acquiring the five treasures ਸੱਤ, ਸੰਤੋਖ, ਦਯਾ, ਧਰਮ, ਧੀਰਜ truth, contentment, righteousness (justice, moral standard, honesty integrity), compassion, patience (tranquillity, fortitude) through Gurmat and onto the state of a Gurmukh. Anxieties, worries and stress will be eliminated. This leads to finally merging with God.

Your question
ਜੇ ਸਭ ਕੁਝ ਰੱਬ ਦੀ ਮਰਜ਼ੀ ਨਾਲ ਹੋ ਰਿਹਾ ਹੈ ਤਾਂ ਪਾਪ ਵੀ ਕਿਉਂ ਨਹੀਂ ਸ਼ਾਮਲ?
now becomes clear.

Hukam is ਸਭ ਕੁਝ ਰੱਬ ਦੀ ਮਰਜ਼ੀ ਨਾਲ ਹੋ ਰਿਹਾ. ‘ਪਾਪ’ is the result of 5 evils described. So, it is ਸ਼ਾਮਲ in Gurbani i.e. 5 evils is a part of God’s Hukam.