In other words, it's not really about the lightsaber (as the related question showed, you can use a lightsaber without the Force. And as numerous examples - including those in this answer - show, you don't even always use the lightsaber in combat as a Jedi. You can kick. You can move. You can even use an uncivilized blaster ala Obi-Wan on Utapau).
The examples are way too numerous to cite, i'll just try a couple.
The Force, like water, takes on the shape of its container without effort, without thought. The water that was Obi-Wan poured itself into the container that was Grievous’s attack, and while some materials might be water-tight, Obi-Wan had yet to encounter any that were entirely, as it were, Force-tight ...
While the intent to swing was still forming in Grievous’s mind, the part of the Force that was Obi-Wan was also the part of the Force that was R2-D2, as well as an internal fusion-welder Anakin had retrofitted into R2-D2’s primary grappling arm, and so there was no need for actual communication between them; it was only Obi-Wan’s personal sense of style that brought his customary gentle smile to his face and his customary gentle murmur to his lips.
He doesn’t even need to reach into the Force.
He has already let the Force reach into him.
The Force flows over him and around him as though he has stepped into a crystal-pure waterfall lost in the green coils of a forgotten rain forest; when he opens himself to that sparkling stream it flows into him and through him and out again without the slightest interference from his conscious will. The part of him that calls itself Obi-Wan Kenobi is no more than a ripple, an eddy in the pool into which he endlessly pours.
There are other parts of him here, as well; there is nothing here that is not a part of him, from the scuff mark on R2-D2’s dome to the tattered hem of Palpatine’s robe, from the spidering crack in one transparisteel panel of the curving view wall above to the great starships that still battle beyond it.
Because this is all part of the Force.
Why is meaningless; it is an echo of the past, or a whisper from the future. All that matters, for this infinite now, is what, and where, and who.
He is all sixteen of the super battle droids, gleaming in laser-reflective chrome, arms loaded with heavy blasters. He is those blasters and he is their targets. He is all eight destroyer droids waiting with electronic patience within their energy shields, and both bodyguards, and every single one of the shivering Neimoidians. He is their clothes, their boots, even each drop of reptile-scented moisture that rolls off them from the misting sprays they use to keep their internal temperatures down. He is the binders that cuff his hands, and he is the electrostaff in the hands of the bodyguard at his back.
He is both of the lightsabers that the other droid bodyguard marches forward to offer to General Grievous.
And he is the general himself.
He is the general’s duranium ribs. He is the beating of Grievous’s alien heart, and is the silent pulse of oxygen pumped through his alien veins. He is the weight of four lightsabers at the general’s belt, and is the greedy anticipation the captured weapons sparked behind the general’s eyes. He is even the plan for his own execution simmering within the general’s brain.
He is all these things, but most important, he is still Obi-Wan Kenobi.
This is why he can simply stand. Why he can simply wait. He has no need to attack, or to defend. There will be battle here, but he is perfectly at ease, perfectly content to let the battle start when it will start, and let it end when it will end.
Just as he will let himself live, or let himself die.
This is how a great Jedi makes war.
General Grievous lifted the two lightsabers, one in each duranium hand, to admire them by the light of turbolaser blasts outside, and said, “Rare trophies, these: the weapon of Anakin Skywalker, and the weapon of General Kenobi. I look forward to adding them to my collection.”
“That will not happen. I am in control here.”
The reply came through Obi-Wan’s lips, but it was not truly Obi-Wan who spoke. Obi-Wan was not in control; he had no need for control. He had the Force.
It was the Force that spoke through him.
He reached through the Force and the Force reached through him; his blade flared to life while still in the air; it flipped toward him, and as he lifted his hands to meet it, its blue flame flashed between his wrists and severed the binders before the handgrip smacked solidly into his palm.
Obi-Wan was so deep in the Force that he wasn’t even suprised it had worked.
He made a quarter turn to face Anakin, who was already in the air, having leapt simultaneously with Obi-Wan’s gentle murmur because Obi-Wan and Anakin were, after all, two parts of the same thing; Anakin’s flip carried him over Obi-Wan’s head at the perfect range for Obi-Wan’s blade to flick out and burn through his partner’s binders, and while Grievous was still flinching away from the fountain of fusion fire, Anakin landed with his own hand extended; Obi-Wan felt a liquid surge in the waterfall that he was, and Anakin’s lightsaber sang through the air and Anakin caught it, and so, one single second after Grievous had begun to summon the intent to swing, Obi-Wan Kenobi and Anakin Skywalker stood back-to-back in the center of the bridge, expressionlessly staring past the snarling blue energy of their lightsabers.