For he hath put all things under his feet. But when he saith, all things are put under him, it is manifest that he is excepted, which did put all things under him.
All things - including death (cf. Ephesians 1:22; Philippians 3:21,; Hebrews 2:8; 1 Peter 3:22). It is said, "hath put," for what God has said is as it were already done, so sure is it. Paul here quotes the 8th Psalm in proof of 1 Corinthians 15:24, end, "For (it is written) He hath put all things," etc. Under his feet - as His footstool (Psalms 110:1). In perfect and lasting subjection.
When he - namely, God, who by His Spirit inspired the Psalmist.