The phrase "outstretched arm" typically means extending or stretching one's arm as far as possible. It can be used metaphorically to describe someone demonstrating strength, power, or authority. Full definition
Is it not striking that the Passover, the spring festival, is one of reminiscence, in which tile devout Jew relives the wondrous experiences of that night when Israel's host went out from Egypt by the mighty hand and outstretched arm of the Lord? (religion-online.org)
For instance, during Pope John Paul's visits to the U.S., you could buy Pope - on - a-rope soap, a Pope watch (like a Mickey Mouse watch, only holier), a Let Us Spray Lawn Sprinkler (a spinning Pope with outstretched arms waters your lawn), and a T - shirt with George, Ringo... and John Paul on it. (redeeminggod.com)
If it wasn't premeditated you would see a bend in his elbow now and then instead of a big outstretched arm in line with his outstretched leg. (justarsenal.com)