All we like sheep have gone astray. "All we" means either the whole nation of Israel, which "went astray" in the wilderness of sin (Psalms 107:4; Psalms 119:176; Ezekiel 34:6), or else the whole race of mankind, which had wandered from the right path, and needed atonement and redemption even mere than Israel itself We have turned every one to his own way.
Collectively and individually, the whole world had sinned. There was "none that did good" absolutely—"no, not one" (Psalms 14:3). All had quitted "the way of the Lord" (Isaiah 40:3) to walk in their "own ways" (Isaiah 66:3).
The Lord hath laid on him; literally, the Lord caused to light upon him. God the Father, as the primary Disposer of all things, lays upon the Son the burden, which the Son voluntarily accepts. He comes into the world to do the Father's will.
He prays to the Father, "Let this cup pass from me: nevertheless not as I will, but as thou wilt" (Matthew 26:39). So St. John says that the Father "sent the Son to be the Propitiation for our sins" (1 John 4:10).
And St. Paul tells us that God (the Father) "made him to be sin for us who knew no sin" (2 Corinthians 5:21). It does not lessen the Son's exceeding mercy and loving-kindness in accepting the burden, that it was laid upon him by the Father.
The iniquity of us all (compare the initial "All we"). The redemption is as universal as the sin, at any rate potentially. Christ on the cross made "a full, perfect, and sufficient sacrifice … for the sins of the whole world."