as it is used in this verse, means,

To save us by paying for our sins.

Only Jesus could do this...
Jesus purchased God's forgiveness for us by His own suffering and death on the cross.
Because Jesus was Himself sinless, He was the only one who was able to save us. By His death, He 'paid the ransom', or, 'delivered' us, from the bondage of sin and the penalties of God's laws.

...Looking for that blessed hope, and the glorious appearing of the great God and our Saviour Jesus Christ; Who gave himself for us, that he might redeem us from all iniquity, and purify unto himself a peculiar people, zealous of good works.
Titus 2:13-14