Macbeth's soliloquy that act1 sc.7 begins with shows how pros and cons of Duncan murder come up thick in his mind. Macbeth hesitates, and the solo speech reveals a self-divided mind.
First, Macbeth knows that the 'deed' is bound to invite dire consequence. If ' the assassination / Could trammel up the consequence, and catch, / With his surcease, success ', he could have killed Duncan at the earliest.
Second, Macbeth also knows that an offender has to receive 'judgement' here in this world itself. If the said 'judgement' were postponed for 'the life to come', Macbeth could have killed Duncan.
Third, Macbeth is further conscious of the 'double trust' that king Duncan is protected with. The killing of Duncan by Macbeth would be a violation of the trust of kinship and the trust of hospitality.
Fourth, Duncan has been mild and transparent in his office as the king, and therefore his murder would arouse great pity for the victim and 'deep damnation' for the killer.
Fifth, Macbeth is afraid of moral isolation, for he has no other reason but 'only vaulting ambition' to kill the good, old king.