Surely. — This seems the best way of rendering the phrase, which literally is if not, and is plainly elliptical, being commonly used to express strong asseveration after an oath.
I have behaved... — The figure here is plain. It is taken from a baby’s first real sorrow when he not merely feels pain, but is allowed no access to that which was his solace hitherto. He moans, and frets, and sobs, but at last is quieted by the love which is powerful to soothe, even when it must deny. So, as George Herbert says of man, “If goodness lead him not, then weariness may toss him to God’s breast.” But the exact rendering is matter of difference and difficulty. The verb rendered “behave” means to make equal or like. This is its meaning, even in Isaiah 38:13, which is the only place referred to by Gesenius in support of his translation here “calmed.” We cannot, therefore, render, as many critics, “I calmed and quieted my soul.” But, as in Hebrew, it is common to express one idea by the combination of two verbs, so “I made like, and I quieted my soul,” is really an idiomatic way of saying “I made as quiet as.” The redundancy of the sign of comparison as after verbs of likening may be illustrated by Psalms 49:12, as well as by the passage in Isaiah referred to above. We thus get: “Surely I made my soul as quiet as a weaned child upon his mother, as a weaned child upon me, my soul.” Instead of fretting after what is too great for him, he quiets his ambition, and his spirit lies calm and gentle, like a child in its mother’s arms, that after the first trouble of weaning is over is soothed and lulled by the maternal caress. Perhaps the opposite idea, expressed by the common phrase, “to nurse ambitious thoughts,” may serve to illustrate this somewhat unwonted image. For Israel as a “weaned child,” comp. Isaiah 28:9.