For Paul’s third argument (Galatians 3:15-18) showing we are saved by faith alone, he changes his approach, saying that he now speaks “in the manner of men.” Paul seems to use logic as a tool to show the Judaizers were wrong in their presentation of legalism as a valid method of Biblical salvation. Logic is a system of deductive reasoning whereby one can assume a conclusion by analyzing the number of principles one knows to be true about a given subject. In this section of chapter three Paul continues his argument of justification by faith alone by showing the logical fallacy of trusting in legalism as a means of obtaining salvation (i.e. justification, sanctification and glorification). Once more, he bases his argument upon our relationship with Abraham.
In Galatians 3:15 Paul uses the analogy of a regular covenant, similar to that of one’s last will, to show that once it is confirmed it cannot be altered, except, of course, by the administrator of the will. The New Testament was confirmed with the death and resurrection of Jesus, but Paul in Galatians 3:16 refers back to another covenant, which God made with Abraham and his seed (Genesis 15:18), meaning with Abraham and his particular descendant, Jesus, the Messiah!
The word seed is a collective noun like the word sheep. It can refer to one or many. How can we be sure that Paul’s argument is valid—i.e. that **seed** refers to Christ and not all of Israel? The argument must refer to the single seed, because Abraham had other children. The promises were not directed to them but to the one seed, Isaac, the child of promise. Yet, all nations were not blessed by Isaac (Genesis 22:18). Therefore, if the promise is good at all, it must refer to a particular seed or descendant, coming after Isaac. That descendant could only be Jesus, because all nations are blessed and brought into a right relationship with God only through him.
Notice that the promises were for both descendants (Genesis 15:5) and land (Genesis 15:18). Abraham was promised physical descendants, but Christ was promise spiritual children, and if they are his spiritual descendants, then by virtue of his physical relationship to Abraham they are also Abraham’s spiritual descendants. Secondly, Abraham was promised land, but Christ was promised a Kingdom. The physical descendants of Abraham inherit the land, but the spiritual descendants (which can be either Jews or gentiles) inherit the Kingdom.
Covenants are either bilateral, where two parties had input in the arrangement, or unilateral where only a single party had input. The covenant God made with Abraham in Genesis 15 was unilateral, that is, it was made by one person, and that was God. He alone walked through the animals and his life alone was security for the covenant between him and Abraham (Genesis 15:17). Notice that there are no ifs in this covenant. Nevertheless, from Exodus to Deuteronomy there are over 350 ifs! The covenant that God made with Abraham was an unchanging covenant, while the Mosaic Covenant was a two sided covenant with both parties equally responsible to keep it (Exodus 24:3-8). It changed constantly from person to person.
Paul makes another point in Galatians 3:17 showing that the Abrahamic Covenant came before the Mosaic Covenant. That is, since the Abrahamic Covenant was ordained 430 years before that of Moses, it couldn’t be modified by that which came later. The Abrahamic Covenant was based upon God’s promise alone. Law keeping wasn’t involved. It was not dependent upon performance of anyone but God. Therefore, if gentiles are Abraham’s spiritual children (through Christ) and not his genetic children, the blessing comes through faith or trusting God and not through anything we do.
Finally, in Galatians 3:18 Paul drives home his point by arguing that if the inheritance was based the Law, then it is no longer based upon a promise, because the promise is unilateral and, therefore, unconditional. However, if the inheritance is based upon keeping a law, then, depending upon the person’s ability and the ease or difficulty of the rules to be kept, it may not be a permanent matter. Nevertheless, it is obvious that God gave the inheritance by promise, not by the Law. The Greek word used for God **giving** the promise to Abraham is kecharistai and is based upon the Greek charis (G5485), meaning grace. It is given in the perfect tense of charizomai (G5483), showing that the gift is permanent.
However, one may ask what “inheritance” does Paul have in mind (Galatians 3:18)? First of all the inheritance includes authority, because Abraham inherits the world (Romans 4:13). Secondly, what we shall inherit is unimaginable for we have no words in which it could be expressed (2Corinthians 2:9). Finally, we are given the earnest of our inheritance in the Spirit of God who dwells within us (Ephesians 1:13-14), which itself opens our eyes to the kind of inheritance we shall have (Ephesians 1:17-18). We are also able to know that it is an eternal inheritance (Hebrews 9:15), incorruptible (1Peter 1:3-5) which allows us to be partakers of divine nature or the very life essence of God (2Peter 1:4; cf. 1John 3:1-2).