Mat 28:18 All power is given unto me in heaven and in earth.

There are two different words that are translated as "power" in the KJV of Matthew. The one used here, exousia, is most frequently translated as "authority" and Christ usually uses it to refer to his power. The first time, in Mat 9:6 as his "power to forgive sins on earth." The other word translated as "power" is dunamis (dunamis), which Christ usually uses to refer to the power of God, the first time in the Lord's Prayer, Mat 6:13. This word, though usually translated as "power" is sometimes translated as "mighty works."

My sense in just looking at Christ's words is that he uses the first word, exousia, to refer to his own authority, while he uses the term dunamis to refer to God's powers. Though he refers to the "mighty works" (dunamis) done in Capernaum (Mat 11:23) and to himself coming down from heaven "with power" (dunamis) in Mat 24:30, both of these references seem to refer more to the Father than himself. He uses the term "power of God" more directly as in Mat 22:29.

Christ uses the term exousia (authority) to refer to the source of John the Baptist's right to baptize in Mat 21:24. In every context, he (and Matthews) uses this with the sense that this type of "power" is given to one person from a higher power.

That is certainly the case here, where Christ says specifically that he has been given this authority. The tense of the verb in Greek is called Aorist, which unlike the simple past tense in English indicates that something was either started or ended at a very specific point in the past as opposed to happening generally or gradually. The inference is that before his resurrection he had certain forms of "authority" from the Father specifically to "forgive sins" (or more accurately "let loose of mistakes") and to teach. After his resurrection, he had "all kinds of authority" or "complete authority." That idea is emphasized by Christ's use of the "earth and heaven," which he uses to refer to all of the universe, both what we see (earth) and what is hidden (sky).

"All" is from pas, which means "all," "the whole," "every," "anyone," "all kinds," and "anything."

"Power" is from exousia ( exousia ), which means "control," "the power of choice," "permission," "the power of authority," "the right of privilege," "abundance of means," and "abuse of power."

"Given" is from didômi (didomi), which means "to give," "to grant," "to hand over," and "to describe."

"Earth" is from gê (ge), which means "the element of earth," "land (country)," "arable land," "the ground," and "the world" as the opposite of the sky.

The other word for "power" discussed here but not in the verse is from dunamis (dunamis), which means "power," "might," "strength," "capacity," "faculty," and "the worth and value of money."