In the spring of the year, the time when kings go forth to battle,
David sent Jo'ab,
and his servants with him,
and all Israel;
and they ravaged the Ammonites, and besieged Rabbah.
But David remained at Jerusalem.
I sort of tinkered with the verse to make it a poem. And as a poem, it is immense in its meaning. David was given every good thing by the Lord. He was given all that was promised to Abraham, to Isaac, Jacob and Moses. What Saul rejected, David was rewared, and with seemingly limitless surplus. When he was hunted, the Lord protected him. When he went to war, the Lord conquered. When he took the city of Peace, the Ark came to him. In all of these things one truth remained constant for David: if he fought, the Lord was his ally.
So David fought and won. Many, many times. David conquered and built and conquered again - all with the help of the Lord. But when David had all the bounty of the Lord that came from his struggles, his desire to struggle became less. Then, in the springtime - a time that could not be better framed by the author of the scripture - David opted out of the struggle to stay within the comforts of the earthly home the Lord had helped him obtain. It was in this place of comfort that he became open to Satan for seemingly the first real time in the story of his life. He rested when the Lord's work was still to be done, and he became immediately vulnerable.
The rest of this story is very pathetic in light of all we know of David before it. The adultery is just the first sin that begins a tale of great tragedy and sorrow for those that David harmed, ultimately resulting in the profoundly tragic death of the son Bathsheba gives birth to. It is David's humility and true penance in the face of his sins that becomes equally profound, showing us again why God chose him over Saul. It also resulted in Psalm 51, the model for all honest pleas for God's mercy.
Time and again in scripture, the Holy Spirit is telling us what we are to be - humble, thankful, contrite, loving and childlike in the presence of the Lord. In 2 Sam. 11:1 the Spirit reminds us that when there is a battle raging for our immortal soul, we jeopardize its outcome by staying home.