The word ADD is used in the Christian vocabulary in a particular way, in that it refers to God’s adding, not ours.

Old Testament H3254
Defines the word ADD yacaph (yä·saf).
A primitive root; to add or augment (often adverbially to continue to do a thing):— add, X again, X any more, X cease, X come more, + conceive again, continue, exceed, X further, X gather together, get more, give moreover, X henceforth, increase (more and more), join, X longer (bring, do, make, much, put), X (the, much, yet) more (and more), proceed (further), prolong, put, be [strong-] er, X yet, yield.  All references.

 Have you ever tried a recipe or a formula in which you added or changed something? You would not expect the results to be as what you may have experienced before.

God’s commandments were given to provide His people a guide to their relationship with Him. His word was enough, with no need for them to augment

“Ye shall not add unto the word which I command you, neither shall ye diminish ought from it, that ye may keep the commandments of the Lord your God which I command you.” Deuteronomy 4;2

His commandments were unsatisfactory for the people in Samuel’s day. God was not enough for them. They wanted what other nations had.

 ^“And all the people said unto Samuel, Pray for thy servants unto the LORD thy God, that we die not: for we have added unto all our sins this evil, to ask us a king.” 1 Samuel 12:19

New Testament G4369
Defines the word ADD  prostithēmi (pros-tē’-thā-mē) From G4314 and G5087; to place additionally, that is, lay beside, annex, repeat:—add, again, give more, increase, lay unto, proceed further, speak to any more.

In the Sermon on the Mount (Matthew 5-7) Jesus taught that life in His kingdom meant that we trust Him for all things, to depend on and live content with what God gives. The first thing needed is to find what was lost in the beginning ~ His kingdom and His righteousness. What He adds will always fit our needs.

“Which of you by taking thought can add one cubit unto his stature?” Matthew 6:27

“But seek ye first the kingdom of God, and his righteousness; and all these things shall be added unto you.” Matthew 6:33

The same word for add is used in Luke 17:5 ~   increase our faith.

How the Lord Adds to His Church
Jesus taught then and now, through His recorded word, how the life of His followers is given and sustained. All that we have is God-given and maintained by His written and Living word within us. In the early church those “that gladly received his word were baptized: and the same day there were added unto them about three thousand souls.” Acts 2;41  

 ^“Praising God, and having favour with all the people.
And the Lord added to the church daily such as should be saved.”Acts 2:47 

Why the Law Was Added
The Commandments were added after the promise of restoration and life that would come through our relationship with Jesus Christ

 ^“Wherefore then serveth the law? It was added because of transgressions, till the seed should come to whom the promise was made; and it was ordained by angels in the hand of a mediator.”  Galatians 3:19  (Read Galatians 3 to get full impact of Jesus as the seed.)

“And beside this, giving all diligence, add to your faith virtue; and to virtue knowledge;”
2 Peter 1:5

We are instructed to add with diligence that by which we are called. (1 Peter 5:10: 2 Peter 1:3) The virtue, knowledge and subsequent attributes are those of our Lord and Savior who, by promise lives within us, by His Spirit working all God requires of us. He is all we need.

Heavenly Father, we praise you that you have brought us full circle from being a disobedient people, wanting to establish our own way of life, to experience the restoration by your grace to know you as Father, Lord, Savior and King of all life. Let the words of our mouths and the meditations of our hearts be acceptable unto you through your Son. We need add nothing except: In Jesus’ name we pray. Amen.

Suggested Reading: First Things that Last Forever