The manner in which God laid our iniquity on Him was that God treated Him as if He had committed every sin ever committed by every person who would ever believe, though He was perfectly innocent of any sin. God did so to Him, so that wrath being spent and justice satisfied, God could then give to the account of sinners who believe, the righteousness of Christ, treating them as if they had done only the righteous acts of Christ. In both cases, this is substitution.