There is no question that only Christ is able to save us from sin. So, how can saints aid us? When we honor saints and ask them to pray for us we are not putting them in the place of Christ. They are close to God, so when they pray for us they seek our salvation from Christ.
Elder Cleopa puts it this way,
When the saints pray for us, it is precisely our salvation that they seek from Christ. They interceded with Him for our salvation. From Christ they entreat our salvation. This is what we mean when we say they intercede for us. By their prayers the saints petition for our salvation -- not, however, as if they themselves have the power to save, for the only one who saves is Christ. Thus we do not venerate saints and angels as we do God. (That which we render the saints and angels is solely a veneration of honor and reverence, while God we adore and worship with perfect adoration which is thus properly called worship)
The apostle Paul reminds us that the saints are our fellow citizens who can help us. "Now therefore ye are no more strangers and foreigners, but fellow citizens with the saints, and of the household of God" (Eph 2:19).
How is we know that the saints have the ability to pray to God on our behalf? We know this from Scripture. "And when he had taken the book, the four beasts and the four and twenty elders fell down before the Lamb, having everyone of them harps, and golden vials full of orders, which are the prayers of the saints" (Rev 5:8)
Some are concerned that the veneration of saints eclipse the glory and honor that belongs to God alone. But God himself glorified His saints. "And the glory which thou gravest me I have given them; that they may be one, even as we are one" (Jn 17:22).
Elder Cleopa says,
No eclipse or depreciation of the glory of God results from the reverence and veneration of His angels. This is so, first of all, because the veneration that we offer God is one thing and the veneration we render to the angels and saints is another. The same Holy Spirit exhorts us to glorify God with His saints saying, "Praise ye God in His saints." Thus we glorify God likewise when we seek in prayer the help and mediation of the angels and saints, since the saints in their succession convey our supplications and requests together with their own prayers to God.
The saints are given special powers by God to work miracles. It says in Scripture, "In the saints that are in His earth hath the Lord been wondrous; He hath wrought all His desires in them" (Ps 15:3). Elder Cleopa lists many examples from the Old Testament of people who were given such powers and then points out the powers of the Holy Apostles, including the seventy, who are able to render all sorts of things.
He writes,
God himself glorified His saints and robed them with His glory: "And the glory which thou gravest me I have given them; that they may be one, even as we are one" (Jn 17:22). Elsewhere He says, "He that receiveth you receiveth me; and he that receiveth me receiveth him who sent me. He that receiveth a prophet in the name of a prophet shall receive a prophets reward; and he that receiveth a righteous man in th ename of a righteous man shall receive a righteous man's reward" (Mat 11:40-41). These statements prove sufficiently enough the delusion of those who repudiate the honor shown toward the saints and angels, -- those beloved servants of God -- not realizing that in practice they turn their back on God himself, the Creator and Fashioner of saints.
Reference: The Truth of Our Faith, 67-77