To your examples, I'd like to point out that God didn't "need" Moses to lift his arm to part the Red Sea either. But with the Red Sea ahead and the Egyptians closing in on them, the Hebrews needed that faith experience.
Indeed, I'm confident that God engineers our circumstances in this mortal life so that we can mature - learning moment by moment to love Him, believe Him and trust Him.
Also, concerning "good works" I'd like to point out that man, particularly Christians, should never take credit for such things. All glory goes to God for without Him we can do nothing.
Therefore when thou doest [thine] alms, do not sound a trumpet before thee, as the hypocrites do in the synagogues and in the streets, that they may have glory of men. Verily I say unto you, They have their reward.
But when thou doest alms, let not thy left hand know what thy right hand doeth: That thine alms may be in secret: and thy Father which seeth in secret himself shall reward thee openly. - Matthew 6:1-4
Then shall the King say unto them on his right hand, Come, ye blessed of my Father, inherit the kingdom prepared for you from the foundation of the world: For I was an hungred, and ye gave me meat: I was thirsty, and ye gave me drink: I was a stranger, and ye took me in: Naked, and ye clothed me: I was sick, and ye visited me: I was in prison, and ye came unto me.
Then shall the righteous answer him, saying, Lord, when saw we thee an hungred, and fed [thee]? or thirsty, and gave [thee] drink? When saw we thee a stranger, and took [thee] in? or naked, and clothed [thee]? Or when saw we thee sick, or in prison, and came unto thee?
And the King shall answer and say unto them, Verily I say unto you, Inasmuch as ye have done [it] unto one of the least of these my brethren, ye have done [it] unto me.
Then shall he say also unto them on the left hand, Depart from me, ye cursed, into everlasting fire, prepared for the devil and his angels: For I was an hungred, and ye gave me no meat: I was thirsty, and ye gave me no drink: I was a stranger, and ye took me not in: naked, and ye clothed me not: sick, and in prison, and ye visited me not.
Then shall they also answer him, saying, Lord, when saw we thee an hungred, or athirst, or a stranger, or naked, or sick, or in prison, and did not minister unto thee? Then shall he answer them, saying, Verily I say unto you, Inasmuch as ye did [it] not to one of the least of these, ye did [it] not to me. And these shall go away into everlasting punishment: but the righteous into life eternal. - Matthew 25:31-46