The Sermon's Missing Word
The word 'love' does not appear in the Sermon on the Mount until the instruction to love enemies.
Matthew 5–7 is 107 verses. The word 'love' (Greek: agapao or agape) first appears in Matthew 5:43–44, in the instruction to love enemies. It does not appear in the beatitudes, the salt and light passage, the law intensification, the instructions on religious practice (alms, prayer, fasting), or the anxiety section. The first use of love language in the longest recorded discourse is in the hardest possible application of the concept. The Lord's Prayer (Matthew 6:9–13), the pivot point of the sermon, contains no mention of love. This is a textual observation; the theological significance is interpretive.
Red Letter Sources
Matthew 5:43Matthew 5:44Matthew 6:9
Ye have heard that it hath been said, Thou shalt love thy neighbour, and hate thine enemy.
But I say unto you, Love your enemies, bless them that curse you, do good to them that hate you, and pray for them which despitefully use you, and persecute you;
After this manner therefore pray ye: Our Father which art in heaven, Hallowed be thy name.
Evidence Notes
Verified by scanning Matthew 5–7 for agapao/agape: first occurrence is 5:43-44 in the enemy-love teaching.