Speed is necessary to overcome the effects of gravity. Throw a ball. It travels along an arc (a parabola) and then hits the ground. The harder (i.e. faster) you throw it, the further it goes before it hits the ground. Now imagine that you could throw that ball a mile; two miles; three miles. Each time you would have to throw faster and faster. Now imagine that you could throw that ball 500 miles. It would land out of side, somewhere beyond the horizon. The arc that the ball follows would begin to approximate the curvature of the Earth. Now imagine that you could throw the ball so fast that it doesn’t just disappear over the horizon, it keeps falling around the curve of the earth. At that point, the ball’s in orbit. It has just achieved escape velocity. This is why high speed is necessary for space flight.
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Orbital velocity is less than escape velocity. Escape velocity is the speed necessary to esacpe gravity, while orbital velocity is what is required to "balance" with gravity.