The following is historical stuff from Francis Turretin. This is not an endorsement of Turretin as a true Christian. Here are some excerpts from Turretin:
“IX. It is proved that this is a true and essential mark of the church. (1) From Scripture, which by this sign distinguishes true Christians as members of the church from false: ‘My sheep hear my voice and follow me’ (Jn. 10:27). Here Christ proves that the unbelieving Jews are not of his fold (i.e., do not belong to the true church) because they do not hear the voice of the shepherd. ‘Ye are not of my sheep, as I said unto you’ (this reason being added), because ‘my sheep hear my voice’ (v. 27). As therefore they who do not hear the voice of Christ are not of his fold, so on the opposite, they who hear and follow him truly belong to it and are members of him.”
Jesus Christ said to the unbelieving Jews:
“But ye believe not, because ye are not of my sheep, as I said unto you. My sheep hear my voice, and I know them, and they follow me. And I give unto them eternal life; and they shall never perish, neither shall any [man] pluck them out of my hand. My Father, which gave [them] me, is greater than all; and no [man] is able to pluck [them] out of my Father’s hand” (John 10:26-29).
There are multitudes of false christs, but only one true Christ. God the Father gave certain sheep to Jesus Christ, the Good Shepherd, and these sheep given by the Father hear and follow the true Christ as an immediate and inevitable fruit of Christ’s having freely given them eternal life.
“X. (2) To the same belongs what Christ says, ‘If ye continue in my word, then are ye my disciples indeed; and ye shall know the truth, and the truth shall make you free’ (Jn. 8:31, 32); ‘He that is of God heareth God’s words’ (v. 47); ‘If a man love me, he will keep my words: and my Father will love him, and we will come unto him, and make our abode with him’ (Jn. 14:23). Here the keeping of the word of Christ and his precepts is set forth as a mark of his true disciples. …However, where Christ dwells with the Father, there it cannot be denied that the true church is, since it is his house and temple. This is confirmed from Mt. 18:20, where Christ promises his presence in the midst of those who are gathered together in his name. For since the saving presence of Christ has place in the true church alone and it is promised to those who are gathered together in the name of Christ (i.e., who assemble by his authority to preach and hear his word), that is undoubtedly the true church where believers come together in the name of Christ. Nor can it be said that ‘it is demonstrated from this passage where Christ is, but not where the church is.’ Christ cannot be found without his church also being found (in which he dwells and which is his body, which cannot be separated from him).”
They who love Jesus Christ in sincerity and incorruptibility will keep His Words; and they who do not love Him will not keep His Words. They who keep the Words of Christ enjoy fellowship with the Triune God of Scripture.
“He that has My commandments and keeps them, it is that one who loves Me; and the [one] that loves Me shall be loved by My Father, and I shall love him and will reveal Myself to him. Judas said to Him, not the Iscariot, Lord, what has happened that You are about to reveal Yourself to us and not at all to the world? Jesus answered and said to him, If anyone loves Me, he will keep My Word, and My Father shall love him. And We will come to him and will make a dwelling place with him. The [one] who does not love Me does not keep My Words. And the Word which you hear is not Mine but of the Father who sent Me. I have spoken these things to you, abiding with you; but the Comforter, the Holy Spirit, whom the Father will send in My name, He shall teach you all things and shall remind you [of] all things that I said to you. I leave peace to you; My peace I give to you. Not as the world gives I give to you. Let not your heart be troubled, nor let it be timid” (John 14:21-27; underlining mine).
“Answering at that time, Jesus said, I praise You, Father, Lord of Heaven and of earth, because You hid these things from [the] sophisticated and cunning and revealed them to babes. Yes, Father, for so it was pleasing before You. All things were yielded up to Me by My Father; and no one knows the Son except the Father; nor does anyone know the Father, except the Son, and the [one] to whom the Son purposes to reveal [Him.] Come to Me, all those laboring and being burdened, and I will give you rest. Take My yoke upon you and learn from Me, because I am meek and lowly in heart, and you will find rest to your souls. For My yoke [is] easy, and My burden is light” (Matthew 11:25-30).
“For this is the love of God, that we keep His commandments; and His commandments are not heavy. Because everything having been born of God overcomes the world, and this is the victory overcoming the world, our faith. Who is the [one] overcoming the world except the [one] who believes that Jesus is the Son of God?” (1 John 5:3-5; underlining mine)