As we say the day approaching, we must not fail to assemble ourselves together.

Some people have gotten out of the habit of meeting for worship, but we must not do that. We should keep on encouraging each other, especially since you know that the day of the Lord's coming is getting closer.
Hebrews 10:25 (Contemporary English Version)

As we approach explaining the concept of assembling ourselves together, let's start with Hebrews 10:22

So let's come near God with pure hearts and a confidence that comes from having faith. Let's keep our hearts pure, our consciences free from evil, and our bodies washed with clean water.

Faith and drawing near to God are inseparable. They go hand in hand.
Faith is defined as coming to God through the hearing and accepting his word, confessing with our mouth, the Lord Jesus Christ. It is believing he  lived, died, rose again and yet lives, sitting at the right hand of God in heaven.

So you will be saved, if you honestly say, "Jesus is Lord," and if you believe with all your heart that God raised him from death. God will accept you and save you, if you truly believe this and tell it to others.
Romans 10:9-10 (Contemporary English Version)

Drawing near Christ we find:

1. Mercy, grace, help
So whenever we are in need, we should come bravely before the throne of our merciful God. There we will be treated with undeserved kindness, and we will find help. Hebrews 4:16 (Contemporary English Version)

because the Law cannot make anything perfect. At the same time, we are given a much better hope, and it can bring us close to God.
Hebrews 7:19 (Contemporary English Version)

2. Salvation
He is forever able to save the people he leads to God, because he always lives to speak to God for them.
Hebrews 7:25 (Contemporary English Version)

3.Sanctification
By his one sacrifice he has forever set free from sin the people he brings to God. Hebrews 10:14 (Contemporary English Version)

4. Cleansing
So let's come near God with pure hearts and a confidence that comes from having faith. Let's keep our hearts pure, our consciences free from evil, and our bodies washed with clean water.
Hebrews 10:22 (Contemporary English Version)

Where there is no prayer and fellowship with Christ, there is no salvation
 

Reasons we are commanded to assemble:

1.As the day approaches trials will come.
Your faith will be like gold that has been tested in a fire. And these trials will prove that your faith is worth much more than gold that can be destroyed. They will show that you will be given praise and honor and glory when Jesus Christ returns. I Peter 1:7 (Contemporary English Version)

2. When we don't meet with other believers we become:
     a. weaker not stronger
     b. susceptible to deceptions and schemes of Satan
 Put on all the armor that God gives, so you can defend yourself against the devil's tricks. Ephesians 6:11 (Contemporary English Version)

3. When we meet, we can:
     a. Exhort one another
     b. Encourage
     c. Give love
     d. Provide for needs
     e. Learn of one another's needs
     f. Provide answers to questions
    g. Get healing

Amen! Amen!