"The sacrificial law designed to teach Substitution" by Charles H. Welch
in The Berean Expositor.


Lev. xvi. 6 -- Before Aaron could offer a sacrifice for the sins of
others, he needed one himself; hence it is plain that if he could not
offer a sacrifice till he had offered one, the law was either an
inexplicable tangle, or it taught substitution.

Lev. xvi.13 -- The cloud of incense, not the blood, preserved Aaron
from death.  Hence, although the typical teaching is, no access to God
apart from atonement by blood, yet, for Aaron's personal safety,
incense is provided.  Incense is a type of prayer (Rev.viii. 3,4). 
Prayer must rest upon a sacrifice; there is no drawing near without the
mercy seat (Num.vii.89, cf. Luke xviii.13, Be propitious - be merciful
- because of atonement), hence, the incense that preserved Aaron must
have received its efficacy by virtue of a far greater sacrifice,
namely, that of Christ (cf. Rom. iii. 24-27).  It follows, then that
(a) One who needs a sacrifice cannot make one, and (b) One who can make
one does not need one.  Hence, it must be made by a righteous one for
unrighteous ones, which, blessed be God, has been done (2 Cor. v. 21; 1
Pet. iii.18).

The blemishlessness of the animal was typical of the righteousness
required for transference in the sacrifice.