And we declare to you glad tidings—that promise which was made to the fathers. God has fulfilled this for us their children, in that He has raised up Jesus. As it is also written in the second Psalm: “You are My Son, Today I have begotten You.” (Acts 13:32–33)

Today’s big question: what does fulfilled mean?

We probably all know the general meaning of the word fulfilled—“to finish or reach the end of something.” We should realize, however, the word fulfill in the context of today’s passage has a much deeper meaning. This word is extremely important and necessary to all Christians. Without this word our foundation for Christianity falls apart. This does not mean we should only use the word when referring to what Jesus has fulfilled, but remembering what the word means in a biblical context is a key principle in understanding the big picture of salvation.

In today’s passage, the Greek word for “fulfilled” is ekpleroo, which means “to fill full or to fill up completely.” In the biblical context, God was fulfilling His promise to provide “His only begotten Son, that whoever believes in Him should not perish but have everlasting life” (John 3:16).

In the Old Testament, God showed the Israelites they could not save themselves—no animal sacrifice was sufficient to atone for their sins (Hebrews 10:4). Only through Jesus Christ would the promise of victory in Genesis 3:15 be fully accomplished. Human beings are fallible, and sadly, when we promise something, we cannot be 100 percent sure the promise will be fulfilled. We should be careful not to make promises we cannot keep or ones we should not give—Jesus spoke about this very topic, warning the Jews about vows:

Nor shall you swear by your head, because you cannot make one hair white or black. But let your “Yes” be “Yes,” and your “No,” “No.” For whatever is more than these is from the evil one. (Matthew 5:36–37)

However, God’s “Yes” is always “Yes.” Jesus would not tell us to do something contradictory to His nature, as “He cannot deny Himself” (2 Timothy 2:13). So when God promised He would raise Jesus up, the Israelites could be sure that it would indeed happen, which today’s passage points out. When God says He will fulfill something, He will always fill it up completely.

Christians should be imitators of God, so we should make sure we never promise something we cannot fulfill. Since we cannot guarantee our promises, we must let our “Yes” be “Yes” and our “No,” “No.” With God, however, fulfill always means “fulfill.” http://www.answersingenesis.org/articles/2011/03/10/what-does-fulfilled-mean