You will know them by their fruit.
v.15 Beware of false prophets by maintaining a healthy balance between not judging (v.1-5) and not being gullible (v.6). They come pretending to have authentic Christianity to conceal their identity/hostility. They do not, however, teach the ‘narrow way’ that leads to life and therefore are leading those who would listen to them to destruction.
v.16a How do we identify these false prophets? You will recognize them by their fruits. There will be many false prophets (Mt 24:11) and they will lead many astray (Mt 24:24).
v.16b-19 This is now illustrated by the image of good trees producing good fruit and bad trees producing bad fruit. A good tree can’t produce bad fruit and a bad tree can’t produce good fruit. False prophets will be judged (as a bad tree thrown into the fire, see Mt 3:10).
v.20 Thus, you will know them (false prophets) by their fruit. At the grocery store we inspect the fruit to discern the good from the bad. The fruit of a person is all one says and does. This fruit will eventually give evidence of the character of the person.

Read Matthew 7:15-20

Ask, seek, knock
For parallel, see Lk 11:9-13.
v.7-8 The three commands (ask, seek, knock) indicate continual, habitual prayer. Persist in prayer with confidence that the Lord will provide according to his perfect will. Be conscience of your dependence on God for his daily provision. The one who asks receives; however, this is not an invitation to satisfy our base desires.
v.9-11 Jesus illustrates with a story. If your son asks for some food, you don’t give him stones. If we, being evil, can give good gifts to our son, how much more will God in heaven give good gifts to those who ask. Our Father, in heaven, is better than the best earthly parents.

The Golden Rule
For parallel, see Lk 6:31.
v.12 The golden rule should come naturally to those who love the Lord with all their heart and their neighbors as themselves, i.e., Mt 22:34-40. Do to others what you have determined reasonable to be done to yourself. This verse is the concluding verse and summary of the material starting in Mt 5:17 which states that Jesus came to fulfill the law and the prophets. He requires the same of his disciples. The rule appears in a negative form in Jewish writings. Carson comments that the goats in Mt 25:31-46 would be acquitted using the negative form of the rule but not under the form attributed to Jesus here.

The Narrow Gate
v.13-14 Enter by the narrow gate. The way of discipleship is the way of opposition, persecution, going against the crowd. The wide gate leads to destruction, but many are they that take this route. See also Lk 13:23-24. The ‘narrow’ way (to heaven) is through Jesus alone; and the ‘wide’ way (to hell) seeks approval of men rather than God. Those who find life will be a minority and will be subject to persecution.

Read Matthew 7:7-14

Judging (not) others
v.1 Only God has the right to judge, therefore do not judge others or you will be judged yourself. The judgment referred to is deliberately pronouncing someone guilty before God.
v.2 If we engage in such judgment, we will be judged by the same measure that we used to judge. That is, you will be treated as you treat others (nlt).
v.3-5 Possibly drawing on his experience as a carpenter, Jesus here uses the metaphor of a log (or speck) in the eye. The message is that honest evaluation is only possible when we are humbled over our own sins. v.1-5 then warn against the judgmentalism that could result from the high standards taught in the sermon.
v.6 Dogs were considered unclean by the Jewish people. “What is holy” refers to the gospel of the kingdom. So therefore, one must make an evaluation of people to determine their true character and avoid continually witnessing to those who will never receive it. This is perhaps, in balance to v.1-5, a warning against naïveté (the opposite of judgmentalism).

Read Matthew 7:1-6

Do not worry about food/clothing/tommorrow.
See parallel passage in Lk 12:22-31.
v.25 Do not be anxious but rather have faith in God. Instead of worry, we are to present our needs to God in faith (Phil 4:6). Worry is uncalled for anxiety. Jesus gives two examples: (1) is not life more important than food? and (2) is not the body more important than clothing? The Lord will take care of our basic needs if we seek first his kingdom and his righteousness (v.33). You cannot serve (both) God and money (v.24); if you choose God, do not worry about the material things money can buy. God will take care of those who follow him with their whole heart. See also 1 Pt 5:7. Don’t fall prey to the materialism of the world (Mt 13:22).
v.26-27 Our worrying cannot add a single nanosecond to our life (and may actually shorten it). Look at the (wild) birds of the air and learn a theological lesson from them (Cf. Jb 12:7-10). They don’t sow or reap yet your heavenly father feeds them. We are of more value to the father than the wild birds (Ps 8:3-8). Birds do what is natural for them in gathering food for the young and building nests, but it is God who actually feeds and clothes them. We too need to do the things that are natural, but to not worry for it is God who will provide.
v.28-30 Lilies of the field are the next example Jesus gives here. They are dressed splendidly though they do not labor after their appearance. Similarly to the above argument, why worry about clothes when God dresses the lilies (which are here today and burned tomorrow).
v.31-33 Do not be anxious about these things (food, drink, clothes). The pagans worry about these things. Our father in heaven knows what our needs are. Worry was a characteristic of ancient pagan religions (we must sacrifice today or he will be angry, etc.). Today, the non-Christian masses worry about such things as diet exercise (to prolong life) and the latest fad in clothing (to look good). Worry about such things demonstrates a lack of faith in God.
v.34 Do not be anxious about tomorrow. Each day has enough trouble of its own. This is perhaps the antidote to thinking we can live carefree. That’s not what the preceding verses say.

Read Matthew 6:25-34