Verse 1
1) "Behold what manner of Love the Father hath bestowed upon us " (Greek idete) means "behold, look upon with comprehension or consider ye "the manner", degree, or kind of love (Divine affection) the Father has (Greek de doken) "given" to us. It was unsolicited, unmerited, and unrequired of Him; yet He gave it, 1 John 4:10; Ephesians 2:4-7.
2) "That we should be called the sons of God". God’s love was given to meet the need of all, while they were yet lost. Note the introduction of the purpose clause (Greek hina) "that" meaning "in order that" we who were not born sons of God might be, become, and/or be called born sons of God. Such is "love Divine all love excelling". John 3:16; Luke 19:10. John then adds (kai esmen) "and we are" – 1 John 3:2; Judges 1:1.
3) "Therefore the world knoweth us-Dot because it knew him not." (Greek dia touto) means, "therefore, through this, or in all this", the world (humanity) does not (know) or recognize us (sons of God) because it did not recognize Him - the Son when He was here. John 1:10-12; John 14:4-7; Acts 13:27.