I stumbled when I saw. Full oft 'tis seen
Our means secure us; and our mere defects
Prove our commodities."
Does not Shakspeare here use secure as a verb, in the sense "to make careless?" If so, the passage would mean, "Our means," that is, our power, our strength, make us wanting in care and vigilance, and too self-confident. Gloucester says, "I stumbled when I saw;" meaning, When I had eyes I walked carelessly; when I had the "means" of seeing and avoiding stumbling-blocks, I stumbled and fell, because I walked without care and watchfulness. Then he adds, "And our mere defects prove our commodities." Our deficiencies, our weaknesses (the sense of them), make us use such care and exertions as to prove advantages to us. Thus the antithesis is preserved.
How scriptural is the first part of the passage!
"Let him that thinketh he standeth take heed lest he fall."—1 Cor. x. 12.
"He hath said in his heart, Tush, I shall never be cast down; there shall no harm happen unto me."—Ps. x. 6.
The second part is also scriptural:
"My strength is made perfect in weakness."—2 Cor. xii. 9.
"When I am weak then am I strong."—2 Cor. xii. 10.
In Timon of Athens we find secure used as verb "Secure thy heart."—Act II. Sc. 2.
Again, in Othello: