If ye have heard of the dispensation of the grace of God which is given me to youward: 3.How that by revelation he made known unto me the mystery; (as I wrote afore in few words).........Whereof I was made a minister, according to the gift of the grace of God given unto me by the effectual working of his power." Ephesians 3: 2-3,7
In Ephesians 3: 2 Paul is saying that God made him (Paul) a minister (Ephesians 3: 3) of the Gospel of grace, which implies also the Gospel of justification by faith.
The definition of the English word dispensation from
https://en.oxforddictionaries.com/definition/dispensation is:
"Origin: Late Middle English: from Latin dispensatio(n-), from the verb dispensare (see dispense)......The action of distributing or supplying something.
‘regulations controlling dispensation of medications..........Permission to be exempted from the laws or observances of the Church.
‘he received papal dispensation to hold a number of benefices’
count noun ‘the Pope granted Henry a dispensation to marry Elizabeth of York’"........... (in Christian theology) a divinely ordained system prevailing at a particular period of history. ‘the Mosaic dispensation’"
However, note that the Oxford Dictionary says in Christian theology a dispensation is a system prevailing at a particular period of history. It does not say that New Testament scripture defines a dispensation in this way.
When dispensationalism says that God made only Paul the minister of the Gospel of Grace and of justification by faith, then dispensationalism gets into problems with the New Testament. There was a point of disagreement between the Jerusalem ekklesia and Paul and his Crew in Acts 15 over circumcision of Gentiles. That disagreement was settled by allowing the Gentile Christians not to have to be circumcised, which agrees with the Gospel of justification by faith and not be race and obeying the law.
In II Peter 3: 15-17 Peter says "And account that the longsuffering of our Lord is salvation; even as our beloved brother Paul also according to the wisdom given unto him hath written unto you;
16. As also in all his epistles, speaking in them of these things; in which are some things hard to be understood, which they that are unlearned and unstable wrest, as they do also the other scriptures, unto their own destruction.
17.Ye therefore, beloved, seeing ye know these things before, beware lest ye also, being led away with the error of the wicked, fall from your own stedfastness."
In his Gospel John uses pisteuo (believe) many times rather than pistis (faith) but the two Greek words have much the same meaning.
https://biblehub.com/greek/4100.htm
Strong's Number 4100, πιστεύω, to believe, have faith in, trust in;"
https://biblehub.com/greek/4102.htm
"Strong's Number 4102, πίστις, pistis: faith, faithfulness
belief, trust, confidence;"
John 3: 16 says "For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life."
Maybe to dispensationalists, in their zeal for dividing up meanings, believers, races, etc, and in their literalist "Hermeneutic," pisteuo has a different meaning than does pistis.
But that third chapter of John's Gospel has a very important New Testament doctrine, "Except a man be born again, he cannot see the kingdom of God" - John 3: 3. Remember that Christ is here talking to a Pharisee, Nicodemus. So, this New Testament doctrine that everyone, regardless of their genetics, must be born again by the Spirit. to enter the kingdom of God means that a Jewish person is not justified by his genetics under the New Covenant. This doctrine itself disagrees with the doctrines established by the Founders of dispensationalism, that the multitude of Old Covenant Israel remain a Chosen People.
But maybe for a dispensationalist the "kingdom of God" is in a different dispensation