The law of inheritance is greater than the law of possession! Abraham's blessings are ours by reason of a covenant promise God made to Abraham (Gen 12:3), (Gal 3:16-18). This promise found it's fulfillment in Christ, and those who are united to Him by the "new birth" into God's family. (Gal 3:29) Since God never breaks a covenant He makes with anyone, this one is still in force!
There were three parts to this covenant between God and Abraham, 1/ the tithe, 2/ walking blameless before God, 3/ offerings. We should take a closer look at each one.
1/ The tithe---In (Gen 14:17-20) we read about Abraham giving a tithe (10%) of the spoils from his victory over his enemies, to Melchizedek, who is a type of Christ. (Heb 7:15-17). This was over 400 years before the law was put in place by Moses. The main scripture on tithing is found in (Mal 3:6-12), where God states His displeasure with His people for not paying their tithes and offerings, and thus bringing a curse upon themselves. As a contrast to a curse, He promises to pour out a blessing on them if they will honor God by bringing the tithe into the storehouse. Our God is Holy, His Word is Holy, and His tithe is Holy. The tithe is God's own personal property, and is not ours to do with as we please. We don't give, or "pay" the tithe, we "return" it to the Lord because it is His. We then have the 90% to live on, and dispose of as we see fit. Our offerings are to be given from this 90%, and can be directed wherever we wish them to go, but the tithe is to go to the "storehouse". In our day this refers to the local church we attend, where we are fed spiritually.
2/ Walking blameless---(Gen 17:1-2) God said to Abraham "serve Me faithfully and live a blameless life" in order to qualify for His blessings. This same qualification applies to us today. To live a blameless life before God means to keep His commandments as outlined in the NT, realizing that this can only be done in the strength of the Holy Spirit who indwells us. We will never be "faultless", or without sin in this life, but we can be "blameless"! These two words have completely different meanings. Thank God, He has made provision for our failures, see (1 John 1:9)
3/ The offering---(Gen 22:1-2) Remember the word "offering" means "to present for acceptance or consideration". In this case Abraham offered his son freely in obedience to God's command, in faith believing that somehow he would be restored to him by God. This is the type of faith toward God that we should be operating in!
Here we see the three requirements for receiving the blessings of Abraham that we are promised as God's children. Remember the requirements must be fulfilled before we can expect to receive the blessings! There are always conditions attached to all of the promises of God. He is not some sort of a heavenly "Santa Clause", just waiting to fulfill all of our selfish requests!