He held IMMENSE personal loyalty of the men who served with him. He was also an aggressive and ambitious general, which if it got him into trouble often, it also saved him too such as at Trenton and Princeton. He also did much to promote effective subordinates such as Greene and Lafayette. And of course he was key in the efforts to professionalize the army and by 1781 his force of a few thousand long service Continentals outside NYC were at least able to meet their adversaries on equal terms, and bolster local less well trained forces.

He also had a firm grasp on the need for the military to be subordinate to civil authority, as exemplified by his repeatedly preventing either regiments or his own officers from marching on the Congress in anger.

While certainly not the whole reason, his relationship with the men who served him shows a lot for his character. A great story comes from a regular enlisted soldier who wrote that he accidentally wandered in to Washington's office Marquee tent at night and was greeted quite cordially despite the interruption. During the winter at Valley Forge he refused to move into the house provided for him until all of the soldiers had received their wood hut accommodations (all were in small canvas tents prior to this). He had great respect for the men that served under him. In the British military officers bought their rank and the separation of classes was much more evident. I would say, however, that much of his deification came in later years. I recommend checking out Inventing George Washington by Edward Lengel, he does a great job of rooting out the sources for the different versions of Washington throughout the years.