Why is Christ's Sacrifice Effective?

Hebrews 10:11-18 NKJV

(11) And every priest stands ministering daily and offering repeatedly the same sacrifices, which can never take away sins. (12) But this Man, after He had offered one sacrifice for sins forever, sat down at the right hand of God, (13) from that time waiting till His enemies are made His footstool. (14) For by one offering He has perfected forever those who are being sanctified. (15) But the Holy Spirit also witnesses to us; for after He had said before, (16) "This is the covenant that I will make with them after those days, says the LORD: I will put My laws into their hearts, and in their minds I will write them," (17) then He adds, "Their sins and their lawless deeds I will remember no more." (18) Now where there is remission of these, there is no longer an offering for sin.