Why did God institute a plan of redemption after Adam and Eve sinned?
God instituted a plan of redemption because sin entered, separating Adam and Eve from God and removing them from the garden. Since God had lost control of what He once owned through that separation, redemption was necessary to buy back and pay the price for that which was lost.
Les teaches that redemption is a matter of buying back or paying the price for something God once owned but lost. In the garden, God had complete control; He fellowshiped with Adam and Eve, and everything was perfect. But sin entered and separated them from God and out of the garden. So immediately God had to institute a plan of redemption to buy back, pay the price for that which He had lost control of. Les parallels this with Israel: when Joseph was sold into slavery by his brothers, sin precipitated their going down to Egypt, where God lost control of His covenant people under Egyptian idolatry, so He would have to redeem them and pay the price to bring them back to Himself.