2:2 propitiation. See also I John 4:10. “Propitiation” in this context means “sacrifice” or “satisfaction.”
2:2 sins of the whole world. The value of Christ’s blood was infinite, sufficient to cover all the sins of all the men and women of every age of history. The fact that it is efficacious unto eternal salvation only for the elect (a term that includes all and only those who believe on Him) is no argument that its value was thereby limited.
2:3 know. This is the first of at least thirty-seven occurrences of “know” (Greek ginosko or eido) in I John. One of the prominent themes in this epistle is the assurance we have in Christ. This first test of how we know our salvation is real is that we desire to keep His commandments just because they are His commandments, and we desire to please Him.
2:5 keepeth his word. This is the second test of life in I John (note I John 2:3). If we are truly in Christ, we will keep (that is, guard) His Word.